QuestionYes, sorry about the confusion. it is a v-twin, 699cc engine. each cylinder has two plugs, so four total.
to do the comp test, I left in the plug that is "deeper" in the head, and hooked the test up to the easily accessible spark plug port. so yes, both front and back tested essentially the same, and the plugs from the front and the rear cylinder had about the same level of gas fouling.
Thanks,
Trale
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Followup To
Question -
Hi again, and thanks for the quick answer to my first question. I tried checking the compression, and each cylinder gave me 170 pounds pressure, plus or minus 3 pounds. When I took the plugs out to do the compression, they were all pretty badly gas fouled, considering that I had only run the machine for about 15-20 min. total since changing the plugs. I think this is because I had it running on choke some of the time; I still can't figure out why it will not rev up. there is just a point where if I try to give it more gas, it stops burning, runs rough, and if I stay on it it dies. Any more suggesstions you could pass along would be great.
Thanks again, Trale
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Followup To
Question -
Hi, I have an 85 VN700. it will start and run, but when I try to rev it up, it dies out at about 2500rpm. I replaced the plugs and cleaned the carbs very thoroughly, to no avail. it still dies out at about 2000 off choke, and with choke on it won't go past 2700. just starts to lug and run very rough when I try to give it the juice.
the plugs all made spark in the open; when checking the vacuum in each carb the front had much less vacuum than the rear. with carbs off, the fron cylinder valve stems looked like they moved much less than the rear, could be an illusion. the fella that had it before said that it had the stuttering problem off idle, but once you got it going down the road it would take off. I havn't ridden the bike yet since I can't get it to run smoothly enough for my liking/safety on the road. I am at my wit's end, any help you can offer would be great.
Thanks Trale
Answer -
Hi Trale, it's a twin right? First, you will need to do a compression test on the engine, disable the ignition coils and test compression with throttle wide open. Let the engine rotate over 5 to 6 revolutions before stopping and reading compression gauge. This will give us a base to go from. Readings should be above 120psi and relatively even between the cylinders. I suspect you might find the front cylinder is lower on compression than the rear. Time to adjust the valves. Thank you for asking and good luck Trale
sincerely
Randy
Answer -
Hi Trale, I am confused..this is a vulcan ? twin cylinder? because you wrote that you took out the plugs to do a compression test and they all looked fouled. Ok, "all" to me is indicating more than "both" did you mean to say "both plugs looked fuel fouled?" you also wrote "each Cylinder head gave good readings. Again "each" indicates more than "both" and my first question to you has yet to be answered. ...it's a twin right?...
once we agree on the engine config we should be able to figure it out in no time..
randy
AnswerOk, cool. Commpression is acceptable. That narrows down our possibilites to either fuel delivery or ignition. The symptoms indicate the engine is starving for fuel at high rpms rather than flooding with fuel, the fact that the choke allows the bike to rev higher indicates a lean condition. Though you said the plugs seem fouled. Factoring the plugs condition in to the equation leads us to loss of ignition/spark at high rpms. Coil saturation failure. Twins vibrate quite a bit...does your machine vibrate more as the rpms increase or does it seem to smooth out as it passes say 2000 rpms. The bike may have developed some loose connectons that manifest under increased rpms. Im afraid without some test equipment you may be comming to the end your ability to diagnose this problem. For example an exhaust analyzer would tell you immediatly if the engine was going lean or rich when it stalls and dies. Lean/stall?
We are focused on fuel delivery. Rich/stall? We focuse on Ignition. One trick you might try is when you rev the engine and it starts to stall...enrichen the mixture by applying the choke...then when it reaches the point it tries to stall again enrichen the mixture more with a can a carb clean, spray the carb clean into the airbox/air intake and see if that cleans up the stall. No? then we have spark problems. Yes? it cleaned up the stall? She is going lean and starving for fuel.. try it and lt me know
randy
