tuning 76 860 GT with K&N filters and Bub Conti-replicas

[JPZ860GT]

Engine is stock with fresh hone, rings, & valvejob. Carbs are stock 32s. Tried 135 mains (stock are 122)... Started nicely from cold, idles fine at first, but gradually starts to load up a little once hot. Also, runs great from idle to redline with no flat spots. Only trouble is subsequent (hot) starts (btw, removed starter, so mine is kick-only), and, more importantly, have to remove plugs regularly to clean up with wire wheel. using NGK B5HS (stock replacement) with stock gap. I also tried 130 and 125 mains with pretty much the same results. An old pro told me to go back to the 122s unless I go with 36mm or larger carbs. Haven't messed with the needle settings at all yet...

[BevHevSteve]

I would bet you need to replace the intake manifold insulators and rebuild the carbs with fresh seal kits, new float needle valves and accelerator pumps. Then properly sync the carbs as per my instructions found elsewhere in this section.....

[JPZ860GT]

Hey Steve,

Thanks for the reply. I rebuilt the carbs with all new seals, and I've done this a couple times now so I'm getting good at it. The kits don't come with accellerator pumps -only a seal that goes around the perimeter of the a-pump diaphram. So, I've been using the original a-pump. The bike only has around 10K miles on it, but a 30-year old a-pump is a 30-year old a-pump. Where can I get those?

As for the intake manifold insulators, if you mean the black rubber seal where the intake and carb meet, then I'm literally stuck. I've tried to get those off each time I've done the carbs. Nogo, those are on there for good -and I highly doubt they let any air by. I have replaced the gaskets where the manifolds meet the heads.

Lastly, I'm not sure what float needle valves are...

[JPZ860GT]

Hello again,

Okay, you can say "duh" now. I spent a few minutes on your site, and now know what a float needle valve is -though I'm not sure I understand how that part would wear out. I also see that you sell a-pumps. I'll order both from you when we thaw out here. I also need to rebuild my petcocks. Do you know what size insert I need? I see you offer 15, 17, and 21 mm. Again, I have a '76 860 GT. Tried making my own, but that didn't work as the material I used was too thick. Thanks,

Jeff

[BevHevSteve]

on the float needle valve - just the tip of it is a hard rubber, I think called VITON, with age it gets harder then doesn;t seal. If there is an indentation around the top where it actually seats against the 'seat' then replace it. Check what # is printed on the brass seat [the part that is screwed into the carb body]

on the taps, you have those square ones right? OK measure the width of the tap, probably 19mm right? They use the 17s

in man insulators are the quarter inch thick rubber between manifold and head. Usually dry out and crack then leak air. Instant foul running when they leak.

[JPZ860GT]

Thanks again Steve, looks like you'll have what I need when the snow is gone. Yeah, I have the square type petcocks. I don't have calipers at home, so I'll take 'em apart and bring them to work so I can make sure I order the right part.

One last question regarding plugs. I've been using NGK B5HS, and I noticed you don't offer those. What's best for my bike?

Thanks,

JP

[BevHevSteve]

That is a pretty hot plug you got there. Standard is the 7, with the 6 being something to use in case you are fowling plugs etc. Hopefully when you get the thing running right you won;t need such a hot plug. I don;t know what the manual calls out for your particular yr/model, but I have the manuals posted on my site which you can check out.........

[JPZ860GT]

The NGK B5HS is indeed the direct replacement for the original Champion L88A. Given my fouling problem, I'll stick with what I'm using. When I worked at a shop years ago, Split-Fire had come out with an equivalent, their SF265F. The bike ran better on those, but, I unfortunately misplaced them at the shop and they don't make those any more. So, back to the NGKs. Anyway, I know that the right thing to do is tune the bike to run on the proper plug -not use a different plug as a band-aid. On that note, I'm still using the stock 1 into 2 throttle wire set-up. I see from your site that the twin wire is the way to fly. I've also read the same advice in Ian Faloon's book on bevel tuning. Interestingly, he also states that it's virtually impossible to achieve better performance with aftermarket pipes and air cleaners on the 860GT. I read that after I bought my free-flowing Bub Conti-replica pipes and K&N filters. So, I'm hopeful that I can prove him wrong next spring. Merry Christmas!

JP