D-Mac project GS550 - more carb issues

[D-Mac]

I think it's time I started a thread here......I'm probably gonna need it. Bear with me, I'm trying to be methodical.

The bike I've been working on is in this thread:

http://www.thegsresources.com/_forum/showthread.php?t=185193

1981 GS550T
K&N air filters (the twin set)
MAC 4-1 exhaust (baffle in)
Dynojet kit - all settings as in the kit (pilot fuel screws 2 turns out; needle on 3rd clip position from top; DJ air jet on the rear of the carb and the DJ main jet installed).

Recap: As some of you might remember from my last post, it was initially idling ok (or so it seemed anyway), but was super-rich at mid throttle (so rich that it would quickly foul plugs and start to misfire within a couple of minutes). I addressed that issue by lowering the needle on spot and putting the spacers/washers on the carbs back to stock (had a much bigger affect of course since the previous owner had moved the spacers under the stock needles way too much - thereby raising the needles a lot. I replicated that setup with the Dynojet needles, so it was far too rich).

Now I'm having a new (?) issue. After only about 20 seconds warming up from cold (and instantly when started warm), the engine is missing a LOT and spraying fuel back through the carbs and into the air filters. The plugs are wet with fuel, and there seems to be a lot of fuel everywhere - especially on carbs 1 and 2 (it's on the sidestand since I removed the centerstand). Pilot jets are stock.

Last night, I thought the fact that my auxiliary fuel cell was hung much too high might be causing some flooding, but fixing that issue (hanging my cell at the position of the normal tank) doesn't seem to have made a difference with my carb problem. I have not allowed the engine to become flooded between tests because I always switch the auxiliary cell off when I'm not running the bike; oil level is normal too. Once running, it just pops like mad. I checked for spark and it's fine (I'm using new coils and I did the coil relay mod during my rebuild). Engine compression remains good. I even pulled the spark box from a spare 550 I have, and it made no difference. The spark plugs don't look too bad when pulled, other than being a little wet with fuel. When I pulled the carbs, there was a lot of fuel in the boots and quite a bit had sprayed back into the air filters.

Under throttle, it no longer bogs down, but the popping remains. It also continues to hang quite a bit at higher rpm. I don't think that's a lean problem but probably a sync issue. For now, I just want to get it running without fuel going everywhere.

Here is what I've come up with so far.

(1) I have a leaking float needle(s). I pulled the carbs and I'm bench testing the float seats now by leaving the aux cell open and hanging above the carbs. So far so good. No fuel leaking down through. I'm gonna leave it for a while to be sure.

(2) Float levels are wrong. I will check the float levels next, but I'm confident I set them properly. I am assuming these should be at stock settings. Any chance that the fact I lowered the front end a couple of inches has changed the angle of the carbs enough to cause problems with too much fuel? I wouldn't think so since it's not like these bikes can't deal with a small incline when riding. Still......maybe?

(3) Pilot fuel screws are simply set too far open. I have each carb set at 2 turns out as recommended with my kit. When the needles were set richer, I had each carb at 2 1/2 turns out (richer) and it idled better than now. I did try turning in a couple of carbs a bit, but the popping didn't improve. I suppose I could have given it more time to "clear out" but I decided to abort before things got worse.

(4) One other disclosure. It does seem to have the tiniest of leaks back at the muffler. I'm gonna fix this as best I can because I know it could make things a little leaner, but the popping at the carbs and apparent flooding I'm getting would seem unrelated (exhaust leak would cause a lean condition anyway, and this one is far back and extremely small). Hell, maybe the fact that I'm running with baffles in is making the circuit too rich? I can't imagine that since the pilot jets aren't different (so basically the jet kit isn't really doing much at idle anyway, right?)

Thoughts?

[Steve]

Have you verified:
1. Valve timing
2. Valve clearance
3. Ignition timing

.

[D-Mac]

Have you verified:
1. Valve timing
Yes- rebuilt the entire top-end and verified this with the manual (and also via photos posted on here).

2. Valve clearance
Yes - all valves are well within spec.

3. Ignition timing
Bike is a 1981 550T, so there are no points to worry about (or I would have suspected that first). The ignition plate looks to be OK. I've run the bike with two different ignitor boxes and no change.

[BassCliff]

Hi,

If the float is sticking on the left carb then that issue could be exacerbated by having the bike on the side stand. I would try to work on the bike standing straight up. Can you borrow a motorcycle stand?




Thank you for your indulgence,

BassCliff

[tom203]

D-Mac said.....
"The ignition plate looks to be OK. I've run the bike with two different ignitor boxes and no change. "

I'd triple check this just to rule out electrical problem- i.e. timing. Check the signal generator coils, substitute a spare set if you got them. check wiring in ignition circuit. Me, I'd bypass the key and kill switches and power the ignition coils direct to be sure of power getting to ignitor.
You could have two bad ignitor boxes.
If you can't borrow a stand, make something to hold bike upright- it will come in handy.

[tkent02]

I think the 81 550 had mechanical spark advance? Either way, a quick check with a timing light would ensure it is advancing correctly. It does not sound like an ignition problem to me, misfiring ignition will not shoot gas back out into the filters, or have fuel pouring out of the boots. It sounds really rich at half throttle, check the needles. Maybe the dyno jet needles are the wrong ones? Try the stock needles just as a troubleshooting tool. If it runs better, or even if it runs too lean that is your problem.

How is it at WOT? Could be the main jets are WAY too big? With CV carbs this would make the mid throttle too rich as well.

Check the fuel levels in the float bowls with the engine running. Too high fuel level will cause problems like these. There is a procedure in the Suzuki manual for this test.

One more thing, did the aluminum plug that seals the 10mm or so hole in the carb body fall out? It's a hole used in the manufacturing process, between the venturi and the float bowl. I had this happen once, it's like having a 10mm diameter main jet, a ton of fuel goes into the engine.

[D-Mac]

Thanks guys!

After leaving the carbs on the bench over night with an open fuel cell hooked up, it seems that the float needles are working fine (no fuel made it through the carbs - I set them up on the same angle as they are on the bike).

Plan of action:

(1) I'm going to re-check float levels next. I might adjust them by lowering the floats 1mm from stock (i.e., increasing the measurement distance measurement from the manual) with my rationale being that I have changed the angle of the carbs by reducing the front-end rake angle - perhaps making things far too rich. Seems a little fishy though since putting a stock GS on a centerstand would result in pretty much the same angle.

(2) I will also check timing when I get the carbs back on. I put on new coils, made new plug wires, and did the coil relay mod too, so I suppose something could be wrong there. I will also start checking into the harness if need be (I had an old Honda once with a bad coil that would start to cause a misfire once it warmed up a lot; I've heard of faulty ignition switches that do the same thing).

I will definitely keep the bike fully upright for future tests.

Lots of consider. I'll post an update after the next round of testing.

[GSXR7ED]

Subscribed.




Ed

[D-Mac]

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 (obviously most important). 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 I took measurements (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?

Could it be the replacement seats/float needles I bought that aren't consistent, or maybe the old floats aren't quite as buoyant anymore? Before dropping another $120 (?) on new floats and seats/needles/o-rings, I think I will try and adjust the floats. Sound ok? I'm thinking there should be roughly a 1:1 relationship between changing float height and fuel height? I guess I'll find out.

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

[tkent02]

Hmmm..... looks like my floats ARE set too high - #2 and #3 especially. Consistent with rich condition and perhaps flooding?

Those are way too close to perfect to be the reason for the HUGE mixture issues you are having.

[tom203]

NIce pics, but your workbench is too clean! and so aren't the carbs. If you have erratic firing (bad ignitor and/or connections), you'd get fuel build up, but I don't see how it's making it backwards to airfilter,Have you checked cam to crank timing?

[D-Mac]

NIce pics, but your workbench is too clean! and so aren't the carbs. If you have erratic firing (bad ignitor and/or connections), you'd get fuel build up, but I don't see how it's making it backwards to airfilter,Have you checked cam to crank timing?

The fuel is being backfired through the carb into the air filter (either the plug is getting fouled, or the timing is off). The "backfires" are not terrible or predictable, and I really don't even remember hearing them the first time I ran the bike (until I revved it and the plugs got badly fouled - before I made the adjustments to the midrange).

I set the cam timing when I rebuilt the engine and I've checked it repeatedly. I was really wary of the tooth being off one cog, so I posted pics here (I also set it one tooth off just to compare, and it was very obvious when I set it correctly/incorrectly). I've set timing on about a dozen similar engines, so I'm very confident that I got it right.

I'm now wondering if maybe I just had a stuck float the last time I hooked up the carbs. When I first rebuilt the carbs, there is a very slight indent in the side of Carb #1 (just above the float bowl), which resulted in me having to trim a bit off the gasket to ensure the float could move freely up and down. I wonder if the float might have been hung up and stuck again. That would explain the fuel being dumped. Of course there appeared to be a lot of fuel dumped into carb boot 2, and still more than I'd consider normal in 3 and 4 too. Hmmm...... Maybe I just had a lot of fuel still in there from my earlier error (hanging my fuel cell too high)?

Too many variables. I think I'm going to set the floats ~1mm lower, re-check the fuel levels, hook everything back up, and run it again. If it's still having issues, I'll check ignition timing to verify it's ok. Then I'll try the electrical (I did the coil relay mod so I have clean power to the coils; the only thing left to do there is bypass the relay to eliminate any issues in the switches, etc. that might be interfering with triggering the relay).

[tom203]

If the intake cam was off by one tooth/pin, and the intake valves are running behind (not closing quick enough) so some mixture would be pushed back thru carbs on compression stroke at least at low speeds. A 550, so was it 19 pins from/including marks 2 and 3?

[D-Mac]

If the intake cam was off by one tooth/pin, and the intake valves are running behind (not closing quick enough) so some mixture would be pushed back thru carbs on compression stroke at least at low speeds. A 550, so was it 19 pins from/including marks 2 and 3?

Yup. That's logical, but I am certain that the intake cam timing is correct (I have the photos to prove it ). I checked and re-checked the cam timing and chain/sprocket position after installing the tensioner and turning the engine over by hand (a lot.....because I had to replace nearly every shim to get the valve lash within spec). If absolutely nothing else makes sense, I will pull the valve cover and confirm it again, but I am sure I set it correctly. I'm about the most OCD person you could imagine with that sort of thing (in addition to having the Suzuki manual, I also have the Clymer and Haynes, and this site of course).

The backfiring didn't happen when I first started the bike and ran it for several minutes....until I started to rev it and it hopelessly fouled the plugs (black). I discovered a good reason why it did that, and pulled the carbs to swap the needle spacers/washers correctly (previous owner had put the plastic spacers under the needle clips, and I had inadvertently copied that pattern with the DJ needles - making it far too rich at mid-throttle). On reassembling everything, I had a much worse popping after only about 20-30 seconds at idle (and almost instantly when I switched plugs and re-started the bike). Popping continued at mid-throttle. Plugs still look somewhat rich, although not as bad as before. Perhaps they just fouled again, and there did seem to be too much fuel getting through to the engine (or an occasional miss can cause a lot more fuel to pile up than I would have imagined). All four exhaust pipes were very hot.

My parts bike is also an '81 550T and it has a signal generator plate/pickup on it, so I can swap that and eliminate(or greatly reduce) the chances that is the culprit. I will first check the timing with a gun to verify it's working properly. The mechanical advancer springs look to be operating ok, but since I have problems at idle now, I don't think they are the answer.

Another thought: On checking the spark, it does seem to look weaker than I would have expected. Perhaps that's my problem? The coils are new Dynacoils (green ones, 3ohm), and I made new wires too (automotive style resistor wires and non-resistor caps). My battery is a new Shorai lithium and it's charged and reading 13v. I don't get why it would be weak with the coil relay mod. I'll did out my multimeter and see if that might be an issue (a bad relay is pretty much all that could be wrong there I'd think).

How about this? Any chance that this backfiring could be caused by a desperate need to sync? I haven't tried to sync because there was a ton of popping, and when I tried last time I started the bike, the fouling was too bad. Maybe the reason it was worse last time I ran it was because my bench sync was worse that time? Pilot fuel screws were at 2 turns out. I did try 1 1/2 turns out at one point to try and lean it out, but it didn't really make a difference.

[BigD_83]

D-Mac,

Maybe I missed the answer earlier in the thread, but what size main jets are you running?