Left cylinder runs weaker than right

[ninskrillz]

Hey guys and gals, I come to you with a problem I've been trying to solve for a couple weeks now. The left cylinder on my 71 is not firing as strong as the right. I believe it is causing inconsistent idle and pop stalling at idle or closed throttle.

I've tried a plethora of things to get it going properly. I've set valve spacing accordingly for my model, swapped plug leads to ensure the pamco ignition was working properly. I've been through the vm carbs multiple times making sure all passages are clear, needle set appropriately, float height correct, float condition perfect, and that the carbs are sync he'd properly.

I have not been able to do a compression or leak down test as I don't have the appropriate tools to do so. Is that my next step? Any other things I can check would be great. Would love to get some feedback if there's anything I'm missing.

 

[TwoManyXS1Bs]

Yep, compression test would definitely provide a direction...

 

[ninskrillz]

Yep, compression test would definitely provide a direction...

Any suggestions for an inexpensive, good tool for the job?

 

[angus67]

you can rent them at most auto part stores. But a basic kit is relatively cheap, and you will have it forever

 

[gggGary]

You can usually feel a weak cylinder with your foot. Get a compression tester with a hose and a couple of adapters, I keep a piece of copper wire on mine, hang it from the handle bar so I can watch it while I kick.

I think I have had this one for about 15 years now. It should hold a reading, if not lube the fittings and shroeder valve with a bit of oil til it does.

http://www.tooldiscounter.com/ItemDisplay.cfm?lookup=MITMV5520&source=froogle&kw=MITMV5520&gclid=CjwKEAiAmeyxBRCJxoKk7IWLl2oSJABvZjhh9DTWXPkF0w7wQ9CWBKp1tYFZBxfby_wScO0BD5sJShoCO-Dw_wcB

 

[ninskrillz]

Ok picked up a tester this morning and used it with good results. After 8 kicks at WOT on each cylinder I came up with 155 on th right and 157 on the left.

 

[ninskrillz]

Derp I just realized I've been saying them backwards. It's the RIGHT cylinder giving me trouble and the LEFT that's fine. I had 157 on the RIGHT and 155 on the LEFT.

 

[gggGary]

Derp I just realized I've been saying them backwards. It's the RIGHT cylinder giving me trouble and the LEFT that's fine. I had 157 on the RIGHT and 155 on the LEFT.

That's one possible problem checked off the list!

carbs timing points condensers coils wires plugs valve setting cam chain setting.

Try swapping sides on the carbs? I spend some quality time tracking down a similar deal with VM's, seems like a throttle cable tank interference causing binding was part of the issue. New float valves might have been part of the fix also.
big ID exhaust pipes and poor running can go hand in hand, see 650 central's exhaust page.

 

[ninskrillz]

Good idea on swapping carbs I'll try that next

 

[ninskrillz]

Ok swapping carbs didn't help

 

[ninskrillz]

did a couple things after work, still no improvement. checked cam chain, pokes out about 1mm, both sets of valves are within spec. the timing was slightly advanced, go it on point. the plugs are black and sooty, could it be possible that a rich condition is causing this?

 

[ninskrillz]

So I found the hose connecting the carb to th manifold was leaking. Replaced it, still running weak on the cylinder but maybe after tweaking the carbs and synching again it will be better. If anyone els has suggestions on things to try in still open to thoughts.

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[wherearewe]

If compression is good and even on both sides (which it is) and swapping carbs didn't make any difference, I would consider electrical possibilities. Maybe one side has a weak spark etc. See if a re-sync helps now you've identified a leaky manifold though.

 

[ninskrillz]

If compression is good and even on both sides (which it is) and swapping carbs didn't make any difference, I would consider electrical possibilities. Maybe one side has a weak spark etc. See if a re-sync helps now you've identified a leaky manifold though.

Yeah I swapped the plug wires and the problem persisted on the right cylinder, so I've ruled out electrical problems.

 

[ridgerunner1965]

did you swap sides with the plugs?

lately ive run into some weird issues with spark plugs that ive never seen in 30 yrs of wrenching on about every kind of engine you can think of.

its a cheap thing to try.

 

[ninskrillz]

did you swap sides with the plugs?

lately ive run into some weird issues with spark plugs that ive never seen in 30 yrs of wrenching on about every kind of engine you can think of.

its a cheap thing to try.

That I did not try. I'll try that now.

 

[ninskrillz]

No difference made in switching plugs between the two cylinders.

Could it be possible the pilot circuits are lean but only causing poor performance with the right carb?

 

[gggGary]

What pipes are on this thing? There have been several reports of collapsed inner exhaust pipes driving guys around the bend trying to out tune that blocked pipe.

 

[ninskrillz]

What pipes are on this thing? There have been several reports of collapsed inner exhaust pipes driving guys around the bend trying to out tune that blocked pipe.

it has single wall 1.5" od head pipes with modified mikesxs dunstall style mufflers

edit: i assume the headers are mikes as well

 

[ninskrillz]

should I consider doing a leakdown test? is that not necessary on account of the good compression test?