At my wits end. HELP!!
Been working on/fighting with my VN750 for weeks now. It is running, and pretty strong, but it still hesitates and misses between 4k and 5k on the tach. No matter what I do, the whole powerband gets better and more solid yet there is still that hiccup. I want to get it perfect!
92 scoot, earshaved and coastered, jetted up, straight pipes (stockers reamed and de-goated), about 12k on the odo. It was running strong a couple of months ago when I developed a fuel leak. Decided to do the rattlecan paint. Brother died. Decided to bolt her up and go. Had rust in the tank I put back on. Sucked the crud through the carbs. Hasn't been right since.
What I have done:
Petcock rebuild. Thoroughly cleaned although no internal parts were changed. It all seemed OK.
Muriatic acid/Naval jelly treatment to the tank to remove rust.
Installed inline fuel filters just above carb intakes.
Tore down and rebuilt carbs thoroughly. Again no gaskets or anything were replaced but they all seemed fine.
Set fuel/air mixture screws carefully to 2 1/4 turns each.
Balanced carbs with home made 2/bottle manometer
At this point I am pretty sure the fuel delivery is solid so I went on to spark and just put in my iridiums that have been waiting. Torqued them to 12 ft/lbs.
It starts well, idles great, has wonderful torque and bottom end. It can make highway speed no problem, but it starts hesitating around 4k and honestly it's never 100% right after that, although the worst of it seems to be between 4k and 5k.
Left to try:
CRobins says I can take the spring out of the petcock and make it gravity feed. I might try this. That way if the problem is somehow the vacuum calling for more gas we can eliminate that.
Bigger in-line fuel filters. These are new since the fuel leak so maybe I just need bigger ones to pass more fuel?
New spark plug wires. I have a set sitting waiting. Been running the stockers and they are cracked and worn.
Dyno2000 CDI. I am starting to wonder if maybe it's the CDI. Maybe it's not calling for the right spark at that time somehow? I don't have another OEA one, but I could replace what I have with the Dyna.
And that's about all I have for ideas. Seems to me the fuel is there and the only way that could be the deal would be if when it suddenly wants more fuel (cranking on it, getting it quickly up to 3k-4k) the fuel can not get there for some reason. Occlusion (too small an opening?) or a vacuum issue? Or if the fuel is there it's not getting burnt- ie ignition issue/CDI or spark cables. But if it were the cables I would expect the problem to be all over and not so consistent. So that doesn't seem likely.
Any other ideas, either for solutions or diagnosis/troubleshooting?
I'm really going mad. I want to get this girl SOLID before I start working on the 1500.
Current VN: 03 VN1600A
Past VNs: 92 VN750A, 98 VN1500A
Future VN: 94/97 VN1500A basketcase/bobber