engine misfire

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ExpeditionImports
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Re: engine misfire

Post by ExpeditionImports »

Hi Guys,

A couple of observations.

Prior to "Tuning" (anything less and you are just wasting your time.....)

#1 - Confirm your jetting is proper for your altitude. Do not assume. Know 100%. The repair manual has a chart which lays out what you should have. Confirm them all.

#2 - make sure your float levels are set properly.

#3 - You must have a timing light (preferably digital and with a tachometer), and a carb sync.

#4 - Idle mixture screws inspected and set at 1.25-1.5 turns out.

#5 - Confirm your ignition system is in good order.

Procedure that I use......

1. Remove the linkages off of both carbs. We want to set up everything initially without the linkages connected.

2. Set the timing. Timing and RPM are directly related. As timing is advanced, RPM will increase and you will have to adjust the idle screws (not Idle mixture screws) out to decrease RPM. RPM should be set at 700-900 depending upon preferences/engine.

3. Carb sync. Using your sync set both carbs to equal vacuum by adjusting the idle screws.

At this point you may be going back and forth to balance sync, timing, and idle. This is the first round of adjustments.

Once the above is set.....you can work the idle mixture screws.

4. - With the engine running take and screw in the idle mixture screw until it is snug. You should hear the engine idle decrease. Screw it back out. Do this on all the screws. If you have a carb where when you screw the idle mixture all the way in and the RPM does not drop I would be looking closely at the float level of that carb and overall condition.

5. - Fine tune the idle mixture screws. This is an art especially if you are not using an exhaust sniffer. Small adjustments on each screw to get the engine to smooth out.

6. - Recheck timing. Recheck sync. Recheck RPM. Adjust as necessary.

7. - Re-attach linkages, adjusting lengths as necessary so that when the linkages are attached you have not changed your sync or RPM. Confirm Sync after the linkages are re-attached. Confirm sync at 1500 RPM.

8. - Check throttle response. Smooth, no popping backfiring.

9. - Confirm with timing light that Timing is advancing to max advance within 2000-2500 RPM.

While in there I will also do the voltage check on the ignition system with it running, just for a baseline.

I did not see the OP using a sync, nor adjusting the idle screws (not idle mixture). Seems like too much attention was being paid to the mixture screws initially.....? I truly mean it when I say it is an art form. Quite often I will have my machinist with 40 years of Porsche experience, come over and fine tune for us. (Even with his experience he brings his sniffer!)

Cheers,

Scott
Expedition Imports Corporation
Vallejo, California
www.expedition-imports.com
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blackstack
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Re: engine misfire

Post by blackstack »

thanks for your reply....and i hope you never have to work on your engine again !!!!!
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edzz
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Re: engine misfire

Post by edzz »

Thank You Scott, 8)

Printed your response and add it to my notes section of my manuals.

Essentially the same thing the manual calls for however a lot easier to follow. 8)
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HawaiianGauer
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Re: engine misfire

Post by HawaiianGauer »

Aloha all-

Sorry for the delays...damn job keeps getting in the way of important stuff! :P As always, I really appreciate the feedback!

Latest update of actions taken since my last post: Per Scott's advice, prior to tuning, I executed #s 4 (1.5 turns out of the CORRECT screws) & 5 on his "prior to tuning" list. Also, idle screws backed out 1.5 turns. I also verified the fuel shutoff solenoids function properly (remove, RPMs drop as cylinder runs out of fuel, reconnect, hear click, cylinder "recovers"). I cannot get the idle below ~1080 as the engine consistently stalls (you can hear a dramatic drop in RPM, like a cylinder or 2 just quit). Timing set to 5 degrees BTDC. All plugs cleaned & reinstalled in same order (they are only a couple of months old). Engine continues to misfire here and there. Sometimes the idle drops dramatically at a stop and the engine stalls. You can tell all cylinders are not consistently contributing.

Go to this link to hear/see what happens as I rev the engine (timing light shows RPMs): http://youtu.be/1ma2QPLva2U Note flames shooting out of rear carb as I rev the motor. Also, recall little to no impact on cylinders 3 & 4 when I pull the ignition cables off the distrib.

Perhaps this is enough info to offer other ideas?

Unfortunately, per Scott's checklist, I have struck out (ie - can't find guidance online or in repair manual; can't figure it out) on the following: 1. Don't know how to confirm my carb's are "jetting properly" at my altitude (sea level; despite having the repair manual); 2. I do not know how to confirm float levels are correct. 3. I do not have a carb sync (reminder: EI synched the carbs in FEB & worked great - I continue to hope/assume carb synching is good). 4. Don't know how to find tune idle jet screws (have not found them yet).

Any advice, guidance, and/or pictures to ID/do these items would be GREATLY appreciated. I'm off the next week and a half and finally have some time to get after this problem again.

The good news I now know the difference between the idle & idle MIXTURE screws thanks to Scott (boy somebody really misled me on a different post...). Anyway, for rookies like me, hope the below helps you positively ID the idle screws. For the idle MIXTURE screws, they are on the other side of the motor near the fuel shutoff solenoids (see repair manual pg 59)
Attachments
gauer idle rpm screws.JPG
gauer idle rpm screws.JPG (71.99 KiB) Viewed 6856 times
Mahalo for your assistance!

Harry X.
73 'Gauer 712M

check out the X-Gauer in action: https://www.youtube.com/watch?v=cYj_UNQDgpM
blackstack
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Re: engine misfire

Post by blackstack »

As I posted earlier my engine was performing exactly as yours.....I did everything you mention except mess with the carbs. My engine now (knock wood) running very nice..no missing or loss of power all cylinders firing(rpm drops when you pull a lead at the cap) etc. I also have a test hill and was happily surprised by how she acts now. I can't put my finger on what exactly did the trick it stopped being weird after i changed the plug wires and thoroughly cleaned the molex fitting. My feeling is that it was a problem connected to the poor contacts at the molex.

Where did you get the voltages for the ignition system check? My readings are 23.6 v at the solenoids, 17-19.6 at positive terminal of coil, do you know if those voltages are within limits? Where else should I check?

I will try to take some pics of the various adjusting screws,

Maybe someone can comment on if the molex red wire could be the cause of the missing etc...I would like to be sure of what i did to fix the problem for next time it happens!!!!

If you look at the entries in this section starting "float level gauge" you can see how to make one,,, made one using a piece of aluminum angle bar and thereby avoided having to make a bend I haven't used it yet and am unsure if i have the level mark correct...i used 1.04 inches from the bottom of the horizontal part of the piece ..(the part that sits on the carb)

I have an old "used but good " synch tool i can send you ..you can send it back ir we can negotiate a price or trade

good luck !
Attachments
synchtool.JPG
synchtool.JPG (49.02 KiB) Viewed 6840 times
floatlevel2.JPG
floatlevel2.JPG (38.69 KiB) Viewed 6840 times
floatlevel.JPG
floatlevel.JPG (36.78 KiB) Viewed 6840 times
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audiocontr
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Re: engine misfire

Post by audiocontr »

I thought I knew what I was doing and quickly learned these carbs are not for the above average tinkerer. From reading your posts, and based on the items which you are unable to test for, I highly recommend sending to Jim. There are way too many variables to account for, and the implied simplicity of the forum posts are misleading.

Now if you're dead set on continuing, here are my recommendations:

Set timing higher than 5degrees. Set it to 9 or 10. See if that helps lower the rpms before stalling
Your carbs are no longer synced. Once you turned the idle screws, you changed their sync. You must acquire a sync tool. The MB/Mini sync tool shown in the post above will not work properly. I have both and tried many many times..
You have found the idle jet adjustment screws at the drivers side base of the carbs. There is one on each corner. It might be external, or they might be internal. (If they happen to be internal, and sealed, leave them alone). You said you turned them the recommended 1.5 turns. Leave them alone. Don't touch until you've fixed the stalling issue.
Is any gas leaking from the seals?
Are you sure the is no vacuum leak or cracked intake runner?
1973 712m
1968 Haflinger
1965 Pathfinder
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HawaiianGauer
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Re: engine misfire

Post by HawaiianGauer »

Whidbey Island - I have/had some military friends there! Man would be awesome if you could put your finger on what you think you did to correct your problem....but understand.

I'm going to try a few things today (double-check valve settings since I had issues there before; gonna take apart the Molex again; will take voltage readings in locations you mentioned; check spark plugs to see if any diff between 3&4 and 1&2). Gonna try again to see if I can figure out/learn about the jets Scott mentioned.

I just re-read Scott's directions, specifically #4 under "procedures I use" - one part says "do this on all the screws". Since I already found out I made a big mistake confusing idle & mixture screws, I don't want to assume anything. How many idle mixture screws are there? I am assuming 1 per carb & they are located under/near the fuel shutoff solenoids. Is that correct?
Mahalo for your assistance!

Harry X.
73 'Gauer 712M

check out the X-Gauer in action: https://www.youtube.com/watch?v=cYj_UNQDgpM
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Jimm391730
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Re: engine misfire

Post by Jimm391730 »

How many idle mixture screws are there? I am assuming 1 per carb & they are located under/near the fuel shutoff solenoids. Is that correct?
No, there are two idle mixture screws on each carb (one for each barrel). They are drivers side front and drivers side rear of each carb, near the bottom, and they angle in towards the center of the carb.

My opinion, after your posts and video, is to:
1. Make sure you have bright, blue spark across the plugs, especially on cylinders 3 and 4. Yellow or Orange sparks show weak ignition. If so, this needs to be fixed before anything else.
2. Double check the valve lash on all cylinders (this could mimic the lack of firing in the rear cylinders, especially at idle if the clearance is too tight).
3. Balance the carbs. It is not as critical as you might think, but your rear carb might be so shut off that no fuel/air is getting to cylinders 3 and 4, hence not much change when you pull their plug wires. All balancing does is ensure that the same amount of air is flowing through each carb and if you are careful and sensitive you may be able to tell by putting a hand over each carb top (with a small opening to feel the airflow) while idling and see if both carbs seem to feel like they have the same draw. Assuming everything else is OK, you can also get some information about the balance by checking the exhaust manifold temps -- cooler means they aren't working as hard at idle, so open up the idle screw on that carb a bit (the screw that stops the throttle arm) until the exhaust temps get more similar.
4. Make sure the gas is dry and does not have water in it. I don't know if you can find it in Hawaii, but in colder areas we have "Heet" which removes water from gas (I think it is mostly alcohol which can absorb water from the gas). Water can come from high humidity of air or water getting into the storage tanks at the gas stations (and some have been known to intentionally add water to increase their profits!). Even a well tuned truck won't run well with wet gas. Water will puddle at the bottom of the tank (where the gas is drawn from) and puddle at the bottom of the carb bowls. With a cool engine, open the covers over the main jets and let the bowls drain out, then refill with known good and dry gas. See if this makes a difference.
Jim M.
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Andre
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Re: engine misfire

Post by Andre »

almost sounds like the mechanical advance is stuck in the distributor as well.
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Mr. Burns
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Re: engine misfire

Post by Mr. Burns »

Aloha
I was having similar issues. " The cross tube drilling is blanked off by external blanking discs. Have any of these blown out by "spit back". With these drillings open the carburetor response will be seriously affected. " viewtopic.php?f=4&t=3284&hilit=carburetor+woes .
On the passenger side of carbs, there are 2 holes that should have blanking discs and 2 that do not. The 2 that should are below the choke, just above where the throttle body bolts stick out. I was missing 1 and it would not idle down. Use a pencil or something w/ a soft tip to probe, as its hard to see.
1 Main jets are 140 for sea level to 5000 feet. You may need replacement seals if you open the cover
2 The float level requires a tool
3. Get a synch tool as you have adjusted the idle screws,
4. Do not adjust idle mixture screws until you have done # 3 ............ you said " Also, idle screws backed out 1.5 turns. " Start w/ 1/2 turn out from when screw start opening butterflies.
5. Looking at the pics of your carbs it looks like the choke is pulled open.
6. The zenith ndix was used by porsche for the 356 and the 32 and 36 are almost identical http://www.scribd.com/doc/39219775/Zenith32NDIX
Good Luck
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HawaiianGauer
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Re: engine misfire

Post by HawaiianGauer »

Sitrep: good progress made yesterday, more lessons learned (may help out other rookies like me? See details below). Current status: running ~85-90% normal; best in probably months. Morale is much higher now!

Current symptoms: occasional misfire (sputter) while maintaining a speed (seems gear agnostic); occasional = ~ every 1/10-3/10 of a mile. Still not 100% power (climbed a highway hill nearby, could not go fast enough to shift into 5th. Before I could slowly accelerate up the hill & shift into 5th gear once speed limit achieved). Runs at idle (after warming up) well – no sputtering/misfiring at all. I finished tinkering with the advance set at only 7 & idle RPMs at ~940-860. I did very minor idle mixture screw adjustments (see below). There is some RPM change when I pull #4 ignition cable from the distrib; there is barely, if any, RPM change when I pull #3. My 3 MAIN questions (there are some more below in the details) for the smart guys:

• Question 1: at this point, I think I can eventually eliminate the now relatively rare misfire AND retain the previously enjoyed 100% power by continued tinkering with timing, idle, and idle mixture adjustments. See #12 below for part of the reason why I think this. Am I kidding myself? Is the perceived lack of RPM change when I pull ignition cables #3 &4 off the distrib telling me something else? Thoughts?

• Question 2: see picture & jet numbers below. I live about 10ft above sea level. Per Mr. Burns, looks like I have the right main jets (#140). Is that correct? What about the other jets?

• Question 3: see picture below. Any thoughts or concerns with the spark plug pictures? I have not seen this before (on any vehicle) – 1 side good, 1 side not so good. Reminder: plugs have maybe 1K miles on them & were installed 4/13.

What I did yesterday:
Since I’ve had problems in the past with valve adjustments loosening and carb sputtering/flames shooting out was limited to the rear carb, I started here:
A. Re-checked all valve adjustments. All were pretty good but 2 were a bit tight. Per previous comments I’ve read, I adjusted slightly erring on the side of a tiny bit lose because I could not get them exactly like the others for some reason. I feel I paid the most attention to detail to date with this episode of valve adjustments.
B. Rear carb: I took the top assembly off. Inspected floats & as many pieces as I could see. Overall, it sure looked like parts were in good shape (Reminder: the carb’s were rebuilt by EI FEB 13). But, I’m no expert so pls see picture below. I pulled out a total of 10 jets & blew air threw them despite looking good. No leaks. Reassembled carb
C. For kicks, I took apart the Molex connecter & re-cleaned the male connections (none looked corroded).

Then I went back to Scott’s check list (my comments in parenthesis):

1. Confirm your jetting is proper for your altitude (still not sure if I have a problem here or not)
2. Make sure your float levels are set properly (can’t do this, don’t have the tool. Reminder: the carb’s were rebuilt by EI FEB 13)
3. You must have a timing light (preferably digital and with a tachometer) (got one), and a carb sync (I got my hands on a carb synch device! Mahalo Scott, my fellow on island 712 owner!)
4. Idle mixture screws inspected and set at 1.25-1.5 turns out (I turned them out to 1.5 turns)
5. Confirm your ignition system is in good order (I think it’s good. Refer to very first post in this thread to see all the ignition parts I’ve replaced in the past 6 months. Volt meter says 20-25 at pos term on coil; fluctuates between 8-10 on fuel cutoff solenoids ->remember, I did the check on the solenoids earlier in this thread – good to go)

Procedure that I (Scott) use......

6. Remove the linkages off of both carbs. We want to set up everything initially without the linkages connected (I did not do this initially. Thought I’d have too hard a time keeping the motor going as I attempted to play with timing advance & idle screw adjustments in an attempt to keep the motor idling and, hopefully, eliminate sputtering so I could use the carb synch tool. I learned later in the day this was a mistake. You can rev the motor, if necessary, from a couple of positions, like the pump lever)
7. Set the timing. Timing and RPM are directly related. As timing is advanced, RPM will increase and you will have to adjust the idle screws (not Idle mixture screws) out to decrease RPM. RPM should be set at 700-900 depending upon preferences/engine (best I could do is idle ~900s. Engine just doesn’t seem to like idling lower – is this indicative of another issue? Best news – as I played around with different timing advance positions & subsequent idle screw adjustments, I found a combo where the misfiring stopped. As Scott says, “this is an art form”. I think I’m turning into an artsy-fartsy guy).
8. Carb sync. Using your sync set both carbs to equal vacuum by adjusting the idle screws (another hard lesson learned – you gotta have this tool. You are kidding yourself if you think you can achieve good carb synching without it. For example, at certain times when adjusting timing & idle screws, how much you turn the screw will have a different impact under different conditions. The only way you can really tell is if you have that tool. I left mine set to ~12, I think that is related to the fact that I could not get the RPMs very low.)

(here is another big lesson learned. While I was playing with timing, RPM with hopes of eliminating misfires so I could use the carb synch tool without fear of flames shooting thru it, I noticed by accident that the rear carb (the one that has nearly all of the misfires/sputtering/flames shooting out) was not returning all the way back to idle. Not sure of the right part(s)/nomenclature…but bottom line is I discovered I had to push the pump lever to get the throttle plates (I think?) to push all the way closed. Just a tiny bit, but it was clear it was not closing all the way like it’s supposed to. Meanwhile, the front carb worked properly – no issue here. Turns out the linkage, the ones I did NOT disconnect in step 6 above, was a bit off. I popped the linkage off and preceded with steps 7 & 8 above. Poof – got rid of all misfires at idle!)

“At this point you may be going back and forth to balance sync, timing, and idle. This is the first round of adjustments. Once the above is set.....you can work the idle mixture screws.”

9. With the engine running take and screw in the idle mixture screw until it is snug. You should hear the engine idle decrease. Screw it back out. Do this on all the screws. If you have a carb where when you screw the idle mixture all the way in and the RPM does not drop I would be looking closely at the float level of that carb and overall condition (all 4 idle mixture screws reacted as expected).
10. Fine tune the idle mixture screws. This is an art especially if you are not using an exhaust sniffer. Small adjustments on each screw to get the engine to smooth out (yes, an art form. I did a LITTLE adjusting but frankly felt I was reaching in the dark. Plus, I was THRILLED that I had eliminated, or so I though, all misfiring. The engine sounded great!)
11. Recheck timing. Recheck sync. Recheck RPM. Adjust as necessary (yes, gotta keep checking these. More artsy-fartsy stuff).
12. Re-attach linkages, adjusting lengths as necessary so that when the linkages are attached you have not changed your sync or RPM. Confirm Sync after the linkages are re-attached. Confirm sync at 1500 RPM (CAREFULLY adjusted the 1 linkage arm & reassembled. Re-checked everything – throttle plate in the rear carb was now closing 100%. MISTAKE I MADE: I did not “confirm sync at 1500 RPM” – I just missed this sentence while I was out there)
13. Check throttle response. Smooth, no popping backfiring (I did, sounded great, no misfiring)
14. Confirm with timing light that Timing is advancing to max advance within 2000-2500 RPM (I cannot say with confidence mine does. What if it doesn’t – what does it mean? Does that answer change if it max’s above 2000-2500 RPM vs below it?)
Attachments
Gauer spark plug and carb 201312.jpg
Gauer spark plug and carb 201312.jpg (135.34 KiB) Viewed 6730 times
Mahalo for your assistance!

Harry X.
73 'Gauer 712M

check out the X-Gauer in action: https://www.youtube.com/watch?v=cYj_UNQDgpM
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pcolette
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Re: engine misfire

Post by pcolette »

Item #5: You mention that the voltage at the fuel cutoff valves is 8-10. This should be close to 24 volts since there is nothing in the ignition system that steps down the voltage to them.
I'm not sure if this has any effect on your issues but the wiring really should be traced back to breaker #10 and voltage checked along the way.
Paul C.
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Jimm391730
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Re: engine misfire

Post by Jimm391730 »

Please confirm that the voltage on the idle solenoids is 8-10 volts, and the voltage on the positive coil terminal is 20-25 volts; it sounds like these could be interchanged? If so, and the positive coil voltage is 8-10V (when running) then you have a bad 4500 rpm box. It was designed to cut the ignition power if the rpm went too high, but these 40+ year old boxes are dying and reducing the coil voltage even at idle.
Jim M.
712W and 710M
compunerdy
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Re: engine misfire

Post by compunerdy »

I have the PinzSSI and I am pretty much having the exact same issues.. Currently mine idles great but will backfire out of the number 4 cylinder through the carb when I get on it. I had the same issue with the rear throttle wanting to stay slightly open and had to adjust the rod to hold it all the way closed and synced the carbs. I have tested the solenoids and they click. If I remove the wire from one when the engine is running that carb will start dripping.. not sure if that is correct or if it even matters since my issues are not at idle and all 4 do the same thing. My current plan is to rebuild or have the carbs rebuilt since I have ruled out everything else as far as I can tell.. I have been following this thread for that easy magical fix I hope you find..
Tim
1975 710K
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HawaiianGauer
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Re: engine misfire

Post by HawaiianGauer »

Jimm391730 wrote:Please confirm that the voltage on the idle solenoids is 8-10 volts, and the voltage on the positive coil terminal is 20-25 volts; it sounds like these could be interchanged? If so, and the positive coil voltage is 8-10V (when running) then you have a bad 4500 rpm box. It was designed to cut the ignition power if the rpm went too high, but these 40+ year old boxes are dying and reducing the coil voltage even at idle.
Love this forum...would be lost without it! Thanks to all!

Jim, confirmed: voltage on pos term on coil 20-25 volts; fuel cutoff valves, confirmed 8-10. Perhaps I'm placing the probe in the wrong spot on the cutoff valves? Or maybe I'm not jamming it into the connector far enough (I barely poked it into the connector out of fear of wire damage)? See diagram below & tell me if my probing is wrong. Also note/confirm part names & #s to ensure we're all talking about the right things:

Tim: I am tracking same (test for clicking when engine is not running; test for decreased RPMs when running & valve cutoff connector removed = carb fuel cutoff system working properly). Also note my carbs were rebuilt by EI ~9 months ago so, unless I see/hear otherwise, I'm ruling out carb rebuild. I'm sticking with timing/RPM/richness combination (the art to find the right combo) as the leading candidate causing my performance/misfiring issues.
Attachments
Gauer fuel cutoff valves.jpg
Gauer fuel cutoff valves.jpg (98.55 KiB) Viewed 6693 times
Mahalo for your assistance!

Harry X.
73 'Gauer 712M

check out the X-Gauer in action: https://www.youtube.com/watch?v=cYj_UNQDgpM
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