83 VT750 Experts Needed

[bigphillip79]

Just got an 83 750 that's been sitting for 3 years. I've done some work so far to get it back to road worthy. So far I've cleaned the carbs, changed air filter, new plugs, oil and filter, final drive oil, coolant flush, and 3-wire fix.
Here's my problem. I had it running, not great but running before the carb kit with just a simple cleaning. Now it is not firing on the rear cylinder. It has no spark. So far I have:
-swapped changed the coils from side to side
-swapped ignitors from side to side
-checked that all connections are tight
All resulting in the same rear cylinder no spark and front good and firing. So I know the coils and igniters are good.
Heres the kicker. Ever so often, after making changes the rear cylinder will start firing and the bike will run good for about 45 seconds or so then it will go dead again and only run on the front cylinder. What am I missing? I'm thinking it's something simple. Well, I hope anyway.
By the way the bike runs good as a thumper. Can't wait to get the front firing so I can tune the carbs and get them balanced.

[stlouisaaron]

Pulse Generator. Do a search on this forum. Had to replace mine this past summer - same basic symptoms. You can run an ohm test on it - but it may or may not give you the right reading. One cylinder not firing - and you've checked everything else (I assume you've also checked your wires?) - then it could be your pulse generator. Not too hard to change - but got to look on ebay or a salvage yard to get one. - Oh yeah, and I'm no expert, but I spent a lot of time wrenching on my 83 750 for the first 18 months I owned it.

[bigphillip79]

Looks like the Pulse Generator for the rear is bad. I have sourced replacements. I have question in getting to them. Looking at the Service Manual I think by removing the entire right side crank case cover i can get at them without removing the clutch. Does that sound right?

If so I would, drain the oil, remove brake pedal, remove right exhaust, remove radiator and right frame section, remove cover and presto, there's the Pulse generators?

In doing some research If anyone is interested in new Pulse Generators. I noticed the Honda PC800 Pacific Coast has a really similar engine to the VT750/700 and also have the 2 cylinder/ 4 plug set up. I checked the Pulse Generators for it and they appear to be almost identical with a different wire routing and are still available from Honda.

[GadgetDad]

In doing some research If anyone is interested in new Pulse Generators. I noticed the Honda PC800 Pacific Coast has a really similar engine to the VT750/700 and also have the 2 cylinder/ 4 plug set up. I checked the Pulse Generators for it and they appear to be almost identical with a different wire routing and are still available from Honda.

If you get the PC800's pulse generators and they work let us know, i got mine from a salvage yard last year and it's been working, but the exposed wire is wrapped in electrical tape so i've just been waiting for it to die on me. Knock on wood though it's been running good.

[bigphillip79]

I ended up using a Gl1500 pulser. A little grinding and wiring splicing and it fit and works great. After the new pulser, throttle cables, choke cable, right handle bar control replacement, carb clean and sync the bike is running pretty sweet. Just gotta do some work on the turn signals, fork seals and brake pads and shoes.

Only running problem I'm having now is the engine is slow to return to idle after throttle is given. I think its running a little lean. Adjusting pilot screw has little if any effect if any on idle unless all the way in. It does have an aftermarket exhaust and we had to make an air filter so I think thats where the problem is. Gonna try restricting the intake just to make sure and maybe up jet from there.

Thoughts?

[BrianVT500C]

Originally Posted by bigphillip79

Only running problem I'm having now is the engine is slow to return to idle after throttle is given.

When I re-installed the chrome cover on the throttle cables (removed to get at the pilot screw) the throttle had the same symptom of slow return - for some reason the cover was was binding the cables, I removed it again and carefully re-installed and everything was good. I have a VT500 so I am not sure you have the same cover.

[bigphillip79]

I don't have the chrome cover but I did make sure the throttle was free and had enough slack to close easily. It snaps back to stop fine and still lags even when returning by hand.

[reno1051]

Originally Posted by bigphillip79

I don't have the chrome cover but I did make sure the throttle was free and had enough slack to close easily. It snaps back to stop fine and still lags even when returning by hand.

my friends 88' radian had a similar issue after he cleaned his carbs. i would make sure all your lines are connected properly and have no vacuum leaks. IIRC, his throttle issue stopped once we fixed a small leak and re-synced his carbs. if you cleaned the carbs and havent checked that they are still in sync, that may be your problem. After re-reading i see you synced your carbs.