plenum or petcock

[ifm61]

I've had my '79 gl1000 nigh on 8 years and it's never disappointed me. Every year at least one thing goes sideways... This year started off with a clutch cover gasket leak, which is a whole lot of not fun, and now on the last couple rides there's been a lot of spluttering, excessive gas use, reduced ability to reach 'speeds' and a fluctuating idle; all of which I've associated with running too 'rich.'

Today I started her up and again it was that spluttering half hearted affair, so I turned off the gas at the fuel petcock. It corrected itself back to that crisp exhaust rip. Turned the fuel back on and the spluttering resumed. Again, once turned off it corrected itself.

Having read a post on another forum where the owner rode his bike through congested areas turning the fuel off and on, I think my problem lies with the plenum seals - I believe Randakks has a replacement kit.

Anyone care to comment?

[pidjones]

Or flooding due to float problems.

[gltriker]

Don't lose anymore riding time. Pull the carburetors off the engine and troubleshoot/rebuild them. Yes. Randakk's is a Very good Kit.

[ifm61]

fao gltriker
if i pull the carbs off that thing, there goes my riding season(s.) c'est finis. i've never worked on carbs before, other than balancing them with a 4 gauge affair, and to be quite honest i think i'd find the learning curve a tad too steep, not to mention the fact i don't have a real garage/workshop or the inclination to sit out in the dolls house it resides in and 'tinker.'
however, that's all my first world problem.
neither of the replies mentioned the chance, however slim, that it could be a fault with the fuel petcock... is it worth my while to look, or does it seem such an obvious carb related issue ie sticking float or faulty plenum seal, that i shouldn't?

[gltriker]

the answer is..... an obvious carb related issue

[ifm61]

damn. on the bright side someone'll make a few bucks off me

[pidjones]

Sounds 100% carb. If mine, they would be off one day and back on the next (but, I have the place, tools, experience, and inclination to tackle the job). There is a tiny chance that a tank full of SeaFoam (MIXED TO LABEL CONCENTRATION) might help. And Randakk once recommended Yamaha carb cleaner (for outboards, I think - connected in-line). I've never tried the Yamaha stuff. SeaFoam has helped a lot with mild build-ups. Primary weapon once they are clean is to only use 100% gasoline, drain carbs when doing lay-up, and store with tank full of 100% plus a good stabilizer. You are burning thus year's fuel, right?

[ifm61]

fao pidjones
just so happens i have a bottle of Seafoam in front of me for that very purpose - where's the harm, right? in the meantime i'm scouting local mechanics

[redglbx]

You have a float valve sticking or failed, do the Seafoam, you just may get lucky. Before you pull the carbs pull the lid off the air cleaner and look down at the plenum floor to see if it’s wet. If it’s dry and the Seafoam has no effect then it’s a bit simpler when you pull the carbs.

You can just pull them and flip them over and pull the bowls, pull the jets and clean them & their circuits well, then I would replace the float valves. Most promote reusing the oe valves but one of the things I’ve found is that the little spring pin in the end fails or gets weak & allows the float to go high and flood the engine, that’s why turning the petcock on/off makes it run better, you’re basically doing the float valves job.

The floats are set to 15.5mm if I remember correctly. Now just don’t use the cheap eBay float valves, save yourself some trouble and buy either oe Honda (expensive) or I’ve had good luck using K&L brand,they seem to be good quality.

Of course once you get them back together you’ll have to re-sync your carbs. That’s about as simple as you can get away with, unless you have a wet (gas) plenum floor then you need to do a complete rebuild & order a good Randakks full kit. Let us know how you do !

[gltriker]

The 'Yamaha Carburetor Cleaner' used to be mixed with gasoline. It was Fantastic stuff!
As I Vaguely recall , at a 3 parts gasoline to 1 ratio. Maybe 2 to 1. Doesn't matter now.

That original Yamaha Carburetor Cleaner formulation was changed to a greener formulation, at least 10 years ago.
( Gasoline was no longer used to dilute the new product. )
With that change, the Cleaner was then mixed with water.
Immersion soaking only became the new process.

I gather you've got more than 8 years of good service out of this set of carburetors.

Yes, there is a plenum seal.
And an unusual shaped seal between each carburetor flange where they independently mount onto the plenum..
See where I'm going with this?
Don't cut corners
Have them serviced carefully and completely.
Repeat after me. I won't cut corners.

*here's a link to what my trike's carburetors suffered from prolonged exposure to a liquid called "gasoline"
go to post # 238. The 1st photo shows the "Plenum seal". The 'unusual' shaped seal located on all 4 carburetors' mounting flange is also presented in 2 photos
viewtopic.php?f=30&t=39996&start=225

*here's a link to the damage that same "gasoline" did to the internals of trike's petcock
go to post# 247
viewtopic.php?f=30&t=39996&start=240

[Dangeruss]

Before pulling any thing apart and messing with the carbs, try this old trick. It only takes a minute or two to try. Sometimes a small piece of crud will get stuck between the float needle and seat. The float will keep pressure on the seat pinching the crud against the needle. Solution is to turn fuel off and start the bike and run out of fuel. The floats will drop and hopefully release the crud pinched between the needle and seat. Turn fuel back on and start the bike. The fuel rushing in to fill the bowls may flush the crud out before the floats rise. Repeat a couple of times if necessary.

May not work, but it’s free, quick and easy to try.

[digger]

I had the same symptoms and it turned out to be the plenum gasket where the two halves meet, you might not need to do an actual rebuild till the riding season is over.

[ifm61]

this forum never disappoints... i had thought about running her dry (as oppose to draining the bowls) just to see what would happen, so that's on the list. i'll also pull the air filter and see how the plenum floor looks. with this information i'll then go to a seasoned pro if need be.
these words from the wiser than me are always much appreciated. cheers.

[gltriker]

with this information i'll then go to a seasoned pro if need be.

You will find several reference articles for Keihin CV type carburetor service purposes in ShopTalk.
Don't allow just anybody to get their hands into your bike's carburetors.

They are not agreeable to ham fisted treatment.

Float hinge posts are easily broken. Fuel bowl retaining screw threads are very easily stripped out of the carburetor bodies.
Pay very special attention to throttle links and choke linkage disassembly and reassembly details.

here's the link to ShopTalk

page/ST

scroll down the left side column to Fuel System

[ifm61]

yup, i read the Randakks post on 'common' mistakes made when attempting this, and stopping reading after 30... hence the seasoned pro comment