1980 GS850GT Won't Run When Throttle opened

[TopGun]

I'm restoring a 1980 GS850GT with 19k miles. BS32SS carbs, transistorized ignition. Probably not been used for years.

It starts and idles OK and can 'blip' throttle OK but when I try to drive it and opening the throttle it flutters and has no power at all.

Action so far:
Cleaned carbs thoroughly several times with carb cleaner, cellulose thinner, pressure line and wire poke following several tutorial videos.
Checked diaphragms with pressure line and vacuum cleaner.
Checked fuel flow by removing float chamber bottom plugs and checked all floats have the amount of fuel.
Balance carbs.
Fitted new rubber manifolds.
Fitted new coils and HT leads now sparks well.
Ignition fine including timing.
Checked cylinder compression and all about 120psi.
Charging is OK.

Local dealer/service shop tells me they have had big problems with carbs needing extensive cleaning and remedies because of blocked passages that are difficult to access.

I would be grateful for any advice or tips.

[Rich82GS750TZ]

See the top 10 list linked in my signature. After reading that, go to BikeCliffs website and download Ed Ness’s Mikuni BS(CV) Carburetor Rebuild Tutorial. Read and follow it. Your shop was right, the good news is you can do this yourself.

[phydeauxmutt]

Two things come to mind:
1. Your "thorough cleaning" was not so thorough. Too many unnecessary chemicals, and the wrong ones, at that. Look at the "BikeCliff's Website" link in Rich's signature. Over on the right side is a tutorial on how to properly clean the carbs. If you haven't done THAT procedure, you haven't done it right.

2. Do you have the air filter connected? Those carbs need SOMETHING bolted to the intake side.

[TopGun]

Hi, Thanks to you and Cliff for helpful replies.

Two items look most promising:
1. Phydeauxmutt's suggestion that carbs must have some restriction on air intake is relevant. The bike only had foam pods, which I understand are considered a problem, and I've left them off. I'll put them back on at least.
2. Cliff's suggestion to look at Ed Ness’s Mikuni BS(CV) Carburetor Rebuild Tutorial is helpful. I have re-read that far more carefully and think there is only one thing I haven't done which is to soak the carbs in a cleaner for a long time, even 24 hours. So together with advice from the service shop I'll try that routine. The shop advised an Ultrasonic cleaner @ 85° in a strong 4-1 solution.

Overall, the message is carbs need more cleaning and I'm sure you're right, Thanks.

[Redman]

,
,
,
,

Local dealer/service shop tells me they have had big problems with carbs needing extensive cleaning and remedies because of blocked passages that are difficult to access.

..

Yes. And that requires "carb dip", a bucket of solvent. Each carb dissasembled and soaked in "carb dip" for 24 hours. As described in tutorial Rich mentioned.

Welcome to THe GSR.

Hey, we need pictures of this G.
Yah, we need to know if it is the maroon one or the black one. (joking)

[Rich82GS750TZ]

It's Rich, not Cliff, but that's OK. Cliff is the guy with the website I linked, and that we all use. And I've been called worse.

Berryman Carb Dip may not be available in the UK, not sure. Maybe some UK members would know of a suitable substitute Carb soak.

[phydeauxmutt]

If you want a quick test, you don't need to re-install the foam filters. Just fold a shop rag in half and hold it over the inlets. If you can, use a zip-tie or two to hold the rag on the outer carbs. Tension will keep the rag out of the inner carbs. Not only should it run better, it will even be good enough to take a ride around the block. I would not do any jetting based on this, but it will at least verify that it runs.

[salty_monk]

Unless the jetting is very different from stock having no filter or the foam filters will certainly give you all sorts of issues with the carburation whether the rack is clean or not

You probably need to work out how they are jetted. Don't trust the numbers on the jets as it's been known for shade tree mechanics to have at them with drills to enlarge the holes.... Good Luck!

[TopGun]

I've found that the bike runs OK'ish now after I removed the plastic rings on the top of the needles to richen the mixture and enlarged the Pilot Jets to .5mm with a drill. Probably need to fine tune this richening. Don't know why but looks as if it's been a mixture problem but that could be caused by something else or perhaps petrol has changed since 1980.
Quite enjoying riding it now, they're nice bikes !

[Ajw78]

Todays gas has had me thinking how much different then in 1978 when my bike was manufactured? Jetting reading plugs is tougher now but maybe just my old man eyes.

[Grimly]

Todays gas has had me thinking how much different then in 1978 when my bike was manufactured? Jetting reading plugs is tougher now but maybe just my old man eyes.

Depends on the gasoline. Here, I find that modern brews only rarely show the range of light tans of classic plug chops. More often, it's a range of greys.

[phydeauxmutt]

I've found that the bike runs OK'ish now after I removed the plastic rings on the top of the needles to richen the mixture and enlarged the Pilot Jets to .5mm with a drill.

OK, all bets are off, and further help is suspended. There is no reference to what the diameter of the hole is in the stock jets, but enlarging with a drill is just plain out of the question. Right now, there is absolutely NO way to know what size jets you have, so any further suggestions will be futile.

[TopGun]

It seems that the problem has been the Pod filters which were on the bike when I bought it and when these are fitted you have to increase the richness of the carbs. because the standard air filter is very restrictive which increases the vacuum suction on the jets.
I have now removed the packing washers above the needles to raise them and drilled the jets larger. The Pilot jets I drilled to .5mm ( not easy ! ) and the main jets to 1.5mm. The bike now runs very well and the performance surprises me. I believe the jet numbers are the size in millimeters multiplied by 100 so the standard #40 Pilot is .4mm and the Main #115 is 1.15mm.
The trouble is that this diagnosing has taken a lot of time.

[TopGun]

Found that .5mm pilots was too large so tried drilling to .35mm which was too small and needed maximum 4 adjuster turns+. Finally I've found that .4mm drilling with 3 adjuster turns is fine so have settled on that now. Starts and runs well at all throttle openings so in summary to make my Pods work:
- Drilled pilots to .4mm.
- Removed packing piece above needles to raise them up.
- Drilled main jets to 1.5mm.