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1974 L-82 4-speed. When cruising or light acceleration around 2000-2500rpm I get this sensation of pulsing and nudging, it’s hard to describe. It sort of feels like the secondaries are wobbling and I get a slight boost then it drops back. The tac and speedo remain constant and do not reflect this. Any thoughts y’all?
St. Jude Donor '11-'12-'13-'14-'15-'16-'17-‘18-'19-'20-'21-'22-'23-'24
I recall having the same problem with my '76 which was years ago. Not sure how a got the fix but I replaced the vacuum can on the distributor which completely solved the problem. The diaphragm inside the can was probably leaking.
It is called trailer hitching and is caused by either improper distributor timing, too much vacuum advance or a combination of both......
Pull hose from vac advance cannister and plug.....drive the car and see what it does......if the trailer hitching disappears....there it is.
At that point I recommend checking timing per Lars papers.......go from there.
Great, thank y'all for the help! I will look into the vacuum advance since I recently switched from port to manifold vacuum so maybe the old diaphragm couldn't handle it.
Hmm, mine did this with my brand new electronic distributor. Turned out to be the weights had the tightest springs on it. Came with 3 sets so I put the middle ones on and solved the issue. I also got the distributor because I was having alot of pinging at 8 degrees timing were it should be, so got a new one hoping it would help. No better on pinging, so research told me to retard the timing. I dropped it to 6 degrees and it made a huge improvement. Still a bit of ping so Im probably gonna try anothe 1 or 2 off the timing. Guess my point is the manuals timing spec isn't always right. Mines say 8 but its clear its gonna be 4 to 6.
I thought I'd post what I ended up doing about this for anybody experiencing this. Now I'm sure the folks and their suggestions above are correct, but my particular issue was caused by a poor air/fuel mixture. I used a gunson colortune and got that engine running just like a song. This trailer hitching issue went away, and significant acceleration increases were felt.
I thought I'd post what I ended up doing about this for anybody experiencing this. Now I'm sure the folks and their suggestions above are correct, but my particular issue was caused by a poor air/fuel mixture. I used a gunson colortune and got that engine running just like a song. This trailer hitching issue went away, and significant acceleration increases were felt.
"Gunson Powertune" ?? Never heard of this tuning tool. Went to their website. Interesting. Can you explain how you used it to tune the AF mixture. Curious. My guess was like others, too much vac advance.
Certainly! I borrowed the gunson colortune from my buddy working on a 240z where he was struggling to get the correct air/fuel mixture with the twin carbs. It's just a spark plug with a glass window where the ceramic normally is, and a little mirror at 45 degrees that lets you actually see the combustion. The tool comes with a little color scale card (like what's in a litmus test) that shows what different colors of the combustion represent. Yellow color meant rich and white meant lean I believe, with the correct mixture giving "bunsen burner blue". I was running very very lean, a couple turns of each screw got me to bunsen burner blue. Super easy, and fixed my trailer hitching hours before I had planned on buying a new vac advance can like y'all suggested haha.
Certainly! I borrowed the gunson colortune from my buddy working on a 240z where he was struggling to get the correct air/fuel mixture with the twin carbs. It's just a spark plug with a glass window where the ceramic normally is, and a little mirror at 45 degrees that lets you actually see the combustion. The tool comes with a little color scale card (like what's in a litmus test) that shows what different colors of the combustion represent. Yellow color meant rich and white meant lean I believe, with the correct mixture giving "bunsen burner blue". I was running very very lean, a couple turns of each screw got me to bunsen burner blue. Super easy, and fixed my trailer hitching hours before I had planned on buying a new vac advance can like y'all suggested haha.
Still doesn't mean your timing and vacuum advance can are right.......even more gains can be had although the engine "seems" to run good........
Still doesn't mean your timing and vacuum advance can are right.......even more gains can be had although the engine "seems" to run good........
Jebby
Yes you are absolutely right. That's why I was dumbfounded when the trailer hitching continued after checking my timing and advance and finding them to be spot on. Looking back, the issue began shortly after I tried to tune the air/fuel mixture "by ear". Shoulda known..
Thanks for that info. Learn something new all the time. I have heard that you need to get your AF mixture sorted prior to setting up timing advance. But wouldn’t the Gunson only give you idle mixture readings?
Glad to help. Yes, this tool is only intended for air/fuel testing. I have always read to get timing fully sorted out before messing with the carb. Here it is straight from the horse's mouth:
05-18-2023, 12:36 PM
What is this “Nudging” sensation felt at cruise?
