'81 GS550 Cafe Build

Just throwing this out there, as it happened to me....

How much oil in on that KnN filter?? I over-oiled mine and the bike ran TERRIBLY rich until I completely washed it out, dried it, and then BARELY misted the filter on the OUTSIDE only with oil.. just barely enough to turn it pink... now I can actually tune it.

If it's over saturated, it's not going to run right.

[cowboyup3371]

Were did you source the new jet needle and pilot jet rubber plugs from? I've been searching the web but I can't find them.

Depending on what bike you have (HINT - Put it in your signature block), you can still find them from Suzuki. Look at the dealer sites like www.gssuzuki.com or www.boulevardsuzuki.com.

Carb parts

Were did you source the new jet needle and pilot jet rubber plugs from? I've been searching the web but I can't find them.

[Sci85]

D-mac, I'm no master mechanic but I agree with tkent02. Float bowls are designed as a "reserve"area for the fuel. They do not meter flow through the carb (that's the job of the jets and needle). Case in point, shut the fuel flow off while the bike is running and it will run just the same until the bowls are almost emptied.

I have not seen a situation where fuel is spit back through the carb on a bike before but HAVE seen this many times on car engines and in each and every instance, it was timing causing the issue (either electrical or mechanical due to improper cam timing setup). The plugs being wet may not be a "fuel" issue at all but the fact that the plugs are not firing properly leaving them wet when you pull them.

If it were me, I would go through the ignition and cam timing with a fine tooth comb. Suspect every part in the loop Until it checks out good. I've even seen bad plug wires create some of the strangest issues. If you had the cams out, I would pull the cover and check the cam timing as well.

Good luck. I know how frustrating these gremlins can seem.

Wow, just wow.

The attention to detail, the time and effort. A superb bike man!

Slightly too high perhaps but not enough to explain the HUGE mixture issues you are having.

The test would be better if it was done with the engine running.

Did you check those plugs between the float bowls and the venturis?

Yeah. I would tend to agree (although my experience with tuning bikes is limited).

I did check and the plugs seem to be ok. I'll post a pic later to confirm we're talking about the same ones.

[tkent02]

Hmmm..... looks like my floats ARE set too high - #2 and #3 especially. Consistent with rich condition and perhaps flooding? I'm going to tinker around with them sometime soon and see if I can get them close to 5.0mm. At least there is hope!

Could it be the replacement seats/float needles I bought, or maybe the old floats aren't quite as buoyant anymore?

I gotta take a break from the fumes. Pretty awful!

Slightly too high perhaps but not enough to explain the HUGE mixture issues you are having.

The test would be better if it was done with the engine running.

Did you check those plugs between the float bowls and the venturis?

Note: I'm cross-posting a similar message with photos and instructions to a thread in the carb section (more people check that one, but I want a record here as well since it's an important part of my build).

So where were we.....?

After fixing the level of my aux fuel source, I still experienced the same problems with the engine missing at idle and even under partial throttle (popping and fuel being blown back through the carbs into the air filters - especially on Carbs 1&2). I checked for ignition issues (swapped ignitor boxes with a spare I have; still need to check timing though, although it's not a points ignition). Admittedly, I started the bike on the side stand (no center stand anymore), so if the float levels were set too high, that might explain why the problem was worse on carbs 1 and 2). A leaky float seat(s) could also explain it. When I pulled the carbs, the was a lot of gas in the boots. Some plugs looked wet with gas. So it was either flooding, or ignition timing (recall that cam timing and valve clearances have been set and triple-checked; bike shows no other symptoms of either of those being wrong).

I pulled the carbs again and left them overnight with my fuel source hooked up and open. No evidence of any float seat leaks. Good.

Next, I measured a couple of float levels to confirm that I had set them right (the measurement made inside the carb between the float and the carb body - gasket removed per instructions; no pics). The measurements I checked were dead on (within 0.05mm of the center of spec = 22.4mm). Yes, I checked on both sides of each float.

After checking the floats, I rigged up a setup to check the fuel levels of the carbs (what really matters to the engine). I set the carbs in a vice on a 7-degree angle (to match the angle they are in the bike) and rigged up my fuel cell to it. I used some vacuum connectors screwed into the float bowl drains to set up the 1/4" hoses to check the fuel levels within the carbs.

Single carb hooked up.


Shows how you take a measurement (note: the photo is approximate - in the case the actual measurement is a little below what is shown - I just held the camera up to give you an idea of what I'm talking about).


Shot of how I took my measurements. Note how carbs 2 and 3 have the highest fluid levels (smaller measurements). You'll see this is my measurements below.


Shot of my testing setup.


The spec is 5.0mm +/- 1.0mm according to the table in my Suzuki manual, although the detailed procedure suggests 5.0mm +/- 0.5mm.

I took an average of 5 measurements made from the edge of the bowl to the bottom of the meniscus (there's my science-geek coming out). I'll spare you the standard deviations.....

Carb 1: 4.54
Carb 2:3.60
Carb 3: 3.75
Carb 4: 4.67

Hmmm..... looks like my floats ARE set too high - #2 and #3 especially. Consistent with rich condition and perhaps flooding? I'm going to tinker around with them sometime soon and see if I can get them close to 5.0mm. At least there is hope!

Could it be the replacement seats/float needles I bought, or maybe the old floats aren't quite as buoyant anymore?

I gotta take a break from the fumes. Pretty awful!

Yup. I'm hopeful this latest issue can be resolved easily enough. If I'm still getting evidence of flooding after lowering the aux tank and fitting new plugs, I'll pull the carbs again and re-test them on the bench for flooding and re-check float heights. The fact that fuel remains in the line right over top of the carbs when the engine is off seems to suggest the float needles are doing something right anyway.

The petcock is OEM and new, and at least it works great (tank is currently sitting on the bench 'on' and not leaking a drop - with a little vacuum pressure it opens and flows well, and it always flows freely on 'prime' as it should).

[psyguy]

lol on the "moron alert"... but we've all done things like that...

yes, the pressure from the fuel supply being that high would likely overcome the (minute) pressure from the carb bowl floats onto the bowl valves... hell, a faulty petcock can be enough for the carb valves to leak...

Actually it's been stated here that having the tank too high will cause issues like that. I found by hooking it on the left side handlebar it works just fine and you won't see any problems.

Great to know! Will do.

[cowboyup3371]

Actually it's been stated here that having the tank too high will cause issues like that. I found by hooking it on the left side handlebar it works just fine and you won't see any problems.

We have a possible "moron alert" here folks......

Look at this photo and see if you can come up with a reason why too much fuel might be flowing through into the carbs.......... I just did.





Give up? Check out how high my aux plastic fuel tank is hanging. I wonder if that crazy height could result in too much fuel pressure when I open the valve on that tank, overwhelming the carb float needles and forcing too much fuel into the engine. I bet that might explain my problems at idle (now that the needle adjustment seems to have helped with the mid-throttle problems). We'll call it "Redneck Rocket Fuel Injection." That might even help explain the problems I've been having with my carb sync tool too (maybe gas running across the vacuum inlets on the carb boots? The inlets are on the bottoms of the boots and fuel drip outs when the sync fasteners are removed). I also seem to recall that the plug fouling got even worse when I hooked up this cell last week, and I've also read in a number of places that an auxiliary fuel source should be "approximately level with the tank height" - possibly for this reason? (and the fact that too low wouldn't exactly work with gravity).

I'm going to put the tank back on, clean the plugs, and see if it helps it run better. If that works, I'll set up my aux source much closer to the carbs.

Edit: You should NOT attempt to do a sync with the Carbtune sync device sitting like it is in the photo. It has to be vertical - preferably hung from a handgrip. I put it there just to take the photo.

Put the carb back on, installed new plugs and fired up the bike for a few minutes.

The Midrange seems better now, but it's still missing after a couple of minutes of warming up and hanging a bit at higher throttle (as it did before). I pulled the plugs and they are wet with gas - a little dark maybe, but not nearly as much as before.

So...it appears that it is still fouling plugs or the ignition timing isn't right (pretty unlikely to be the latter- it's not a points ignition, plus the missing isn't happening on startup or in any consistent way).

I'm wondering if the float level might need adjustment. It's on spec, but do you think that lowering the front end of the bike so much would cause too much fuel to enter the carb bodies? Weird hypothesis I think. I will try and adjust the fuel pilot screws and re-sync first.

It's looking more like I might take it to the dyno....

Seriously D-mac, love this bike. I envy the mass amount of tools and cleaning gear you have access too (more so the cleaning equipment).

On a side not, if you want a louder exhaust first try messing with the baffle/packing in the muffler. If I'm not mistaken (since I have never looked into it to be honest) it may have a very restrictive packing/baffle. Search around, and I'm sure you will find something.

Again, damn amazing project D-Mac. I will be praying mine will turn out HALF as good