need help with a rich/ lean issue.

[trojanjohn]

Hey there awesome people. John from little ole England here,
Im looking for a little help with a fueling issue to the carbs. So, my sons 1981 DOHC, he's on active duty in Afghan and I promised him Id get it running sweet before he returns in November. Its bored out to 823cc because I had to, Wiseco pistons. k and n pods, Delkevic 4 into 1 exhaust, not baffled. Dynojet stage 3 kit. whole engine re built. Carbs stripped cleaned ultrasonically twice. Acceloraters all new, as are floats valves needles and jets. Great spark on all 4, timing is good. great compression, great leakdown test results. Custom tank with 5mm petcock outlet (quality after market pet cock listed for cb750s) and as you know, 8mm fuel pipe into the carbs between no 1 and 2. Bench synced. Idles and revs in the workshop lovely. Valve clearances check and re checked.
No matter what i do i am constantly getting rich to very rich plugs at 1 and 2 perfect at 3 and lean to very lean at 4. could it be that I'm low on fuel delivery as I'm now asking for more than the petcock can deliver with the bigger bore and stage 3 kit ???.
I have a slight leak on carb boot no 1 and when sprayed with starter fuel she bogs down rather than increases in revs, as you would expect if rich. Also when I pull the choke while riding she bogs down. All fuel pipes checked, no blockages. Idle screws all at 3 1/2 turns.
Having never had an engine bored before, or fitted a stage 3 kit, i was wondering if fuel delivery is an issue?
Really looking forward to some knowledge from you good people. Much respect.

 

[amc49]

The compression needs to be around 150 psi plus and 170 is the book number. The carb manifolds must be new, if one is cracked they all likely are. People clean the carbs up to 5 times and still not right, just doing it guarantees nothing. Sonic cleaning a waste. If the flat covers on left side not yanked to check the aircuts then you could have whopping vacuum leaks right there. You need to defeat those. I'd back the idle needles back down to 2.5 turns.

Dynojet kits ( a story right there about the particular kit for these engines) are crap and the needles on stage 3 the worst. The jets have bigger numbers on them to make you think you are doing something but the actual holes are smaller than Keihin jets at same number. No mention of if the slides were drilled out.

Removing the OEM airbox is almost always a big mistake, the carbs lift the slides faster using it and K&N filters just give utter fits. Slower slides then send the carbs rich. I CAN tell you that if you are not real close with stock Honda parts using 75 pri and 115 sec jets and dead stock needles you have something wrong using K&N. The bike with that setup should run fine, plugs light tan and rev to 9500+ rpm. The K&N may stop it from pulling out 100% in top gear when the slides refuse to open all the way, what the K&Ns do. The OEM paper filter in airbox is just enough restriction to induce the slide to fully open up. The slides also open faster when all carbs are connected to a common box, they then share vacuum drop to make it more forceful and the slides then work very fast and on time.

Do that and bump the timing advanced say another .030" above the OEM mark and even more help.

The OEM carb idle circuits are whacky, they are linked together with the primary circuits and the idle jet (pilot) clogged will be super lean but then as soon as you open throttle the slightest amount you switch to primary and the clogged idle then makes the primary go super rich because the pilot system is used as an airbleed when the system switched to primary. You MUST ensure 100% that the pilot jet is open, using smallest string in a guitar, the E string, which is the perfect .013" needed for that restriction.

Boring bigger only accentuates what I already said. No real change.

Petcock could be an issue, I never had trouble on my '80 DOHC 750F using the smaller one than came OEM on the '81. But it was the exact same on used on my CB550F which I did have trouble with being too small. Honda at some point realized there was an issue there, they enlarged the petcocks twice. Petcock of course will lean you not richen.

Say, tell that lad of yours a great many thanks with helping us out over there with that mess. I'm sure he doesn't hear it nearly enough. We got that idiot Trump over here to muck things up, he could care less. About ours much less yours.

 

[trojanjohn]

Thanks amc49 for a ton of useful info, it's good to have you on board. I have read some of your posts before and I know you are not a fan for scrapping the oem airbox, and I respect that. But it's gone and I've invested too much time to quit now.
So, the slides are drilled as dynojet instruction.

To confirm, you reccomend fitting 75/115 jets and refitting the stock needle, idles to 2 1/2 turns, all with K and Ns?? If that's right, I'll get on it,

I'll make sure the pilot is not clogged.
The intake boots are all new, just got a bad clamp so waiting for a new one from David Silver Parts.
The carbs were broken down twice to individual parts and cleaned after the ultra sonic, even the press fit jets, so I'm fairly confident they are good.
I'll pass on your good wishes to my son, it's a proper shitshow out there, but not as bad as it used to be. No one cares here in the UK about servicemen and women, we could learn a thing or two from you guys about respect.
Thanks again.

 

[amc49]

'...you reccomend fitting 75/115 jets and refitting the stock needle, idles to 2 1/2 turns, all with K and Ns??'

Yes, the engine MUST be solid though, so much of the performance depends on it, the CVs on these are super sensitive since they are not the rubber diaphragm type. The engine draw (vacuum) must be great to open them up. Drilled slides won't hurt when carbs reverted back to mostly tock, the drilling still helps.

Odd about the '81 carbs still being pressed jet pilot, here they went to screw-in type that year. I was also under the impression all Euro carbs had no accelerator pump on them, the way it's been so far.

 

[trojanjohn]

Hi
Thanks for that. I'm not sure the carbs are original to this engine. The whole thing is a mish mash of bits and bob's and bent frames and came in boxes, with a fatboy tank!.
Thats why being so close after all the work is a near miracle in itself. Loved and loving every minute though. But I will never put pods on a dohc again
Thanks a million for the help.

 

[mrdrhawk]

I also am running 4 inti 1 with pods so I tried your recommended jetting from my 110-70 1-3/4 and noticed an immediate improvement,

plugs are coloring up nicely. Thanks for info.