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78 GS550 With Wrong Carbs

  • Thread starter Thread starter sbbloom69
  • Start date Start date
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sbbloom69

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HI,
I just joined, refered by bexabarr (thanks!), did some searches and found most of what I need.

I still have 11 pages to sift through on "GS550 carbs" so thought I would try the direct route.
I picked up this 78 GS550 in March, sat for 2 years. Northern New Mexico is very dry. No rust on anything, but the low humidity tends to varnish carbs quickly. Stock exhaust, stock aircleaner.

Only after I got my 78 GS550 home ($200), replaced the tank with a used, but clean one, changed plugs, points, condenser and set the gaps, static timing etc, cleaned and rebuilt the petcock, replaced the coils / wires (all parts from local guy or ebay), and did a QUICKY carb clean (pulled bowls, checked floats and float valves, carb cleaned and air-blew the passages) did I try to start the bike. It started and runs fair WHILE COLD. After warmup, sputters, won't idle, and tries to die. Looking at plugs, very dark and fluffy (RICH!). This makes sense since it runs ok cold (when you need rich).

Anyway. After all that, I finally get a Clymer book and discovered that my 78 should have the VM carbs. I have the CV's!!!! The bottom of one of the bowls had yellow marker "82 550".

So, I obviously have CV carbs from some type of 1980ish Suzuki on my 78 that is supposed to have slide carbs. (BTW, I have done my pennance on carb work, to include 2-strokes and 4-strokes. My favorite is my current superbike, my Honda CBX....6 CV beasts!)

I read in one of the threads here that a later GS550 CV carb set absolutely doesn't mate with the 77-79 GS550 head / carb boots, yet my air cleaner and box appear stock, as do the boots to the head.

So what are my options? I"m going to start with a proper, deep cleaning, mixture screw check, etc, and go from there.

Should I attempt to rejet the CV's (yeah, I know I'm asking for hell)? Should I try and find a set of original VM's and clean/overhaul them?


Ooo..... just a BAD thought. What if my entire engine isn't a 78? The engine number is "not readable". Is there a way to tell engine year without the engine number? It still has points, so that makes it a 77-79?? Did Suzuki go to CV carbs the same year they went to CDI (80)?

Anyway, set me straight guys. I'd really rather not play jets and needles if I'm just ****ing in the wind.

Stuart in New Mexico
78 Suzuki GS550
79 Honda CBX
72 Honda CB350F
 
Hi Stuart,

Welcome to the the site. As to identifying your engine-does it have a kick starter? GS550's had kick starters until 1979. If yours doesn't the engine is probably been replaced with a newer 1 OR the head was replace with a later one that would accept the CV carbs.(that's how it works with the 850s anyway).

Hope this helps a little.

Scott
 
The VM series carburetor has an elongated 1" x 2" top that is held on by 3 phillips screws (4mm). The CV style Mikuni carbs have larger and squarish tops that are held on by four phillips screws (5mm). I am pretty confident you couldn't mount the constant velocity carburetors using VM style intake manifolds due to the much larger venturi diameter of the CV carbs (BS series I think). If you can mount them on the stock intake manifolds and airbox, they will be VM carbs.
 
Scott, you may have resolved it.

I don't have a kick starter. Wow....

Here's what I have:
CV Carbs
Points
No Kick Starter
ground off engine number

No offense to wiredgeorge, but I KNOW the difference between the CV and VM carbs. I have the CVs. I have cleaned and overhauled carbs on the following bikes starting with my 1972 Hodaka B+

72 Hodaka, 73 Honda CL350 (Twin w/ scrambler pipes), 75 Honda CB750' 74 Suzuki GT-750 (Water Buffalo or Kettle)' 69 Suzuki GT-500 Titan, 72 Yamaha R5 250, 79 Honda CBX (still have this one!), 78 Suzuki DR370, 78 Honda XL250S

Plus various Evinrude, Johnson, Buccaneer and Honda outboards.

I now know a 78 Should have the VM22SS Slide carbs (77-79)
80 - 82 have the BS32SS CV Carbs (Diaphragms)
83 - on have the BSW30SS 2 barrelled carbs.

My bike has stock exhaust and stock air filter box, filter, plastic air box behind the carbs. Everything appears to mate up correctly (I've already pulled and reinstalled the carbs once). I can understand how the 2-barrelled BSW30SS carbs won't mate to a 78, but will the 80-82 CV carb bores mate up to the rubber intake manifold boots on a 78? Are the heads actually different between the 77-79 series and the 80-82 series (spacing or diameter)? Wiredgeorge says the CV bores are bigger than the VM bores. Can this be accommodated if someone put 80 intake boots (to match the 80 CV carbs) on a 78 head? Are the 77-79 heads the same as the 80-82 with just the boots different?

Again, the carbs go on and pull off OK on the intake boots. The airbox boots slip on and off the back of the carbs OK.

All I know is I have CV CARBS (that someone marked with a yellow marker saying 80 GS550), I have POINTS, and I have NO KICKSTARTER.

I supposed there is a chance I have a 78 frame, an 80/81/82 head and carbs, and a 79 Lower Engine (combination of points and no kickstarter)??

Frame Number (partial) GS550-1139XX. What's left of the VIN sticker says it was manufactured in 11/77 (should be a 78 right?)

I looked at the bike last night, the original no-tamper plugs are still installed in the mixture screw holes (holes just FORWARD of the diaphragm) There is no ID number on the carbs that I could see, just Mikuni / Kogyo and Japan.

I still think I'm going to pull the carbs again, do a deep clean, record all the jet numbers, etc, and then decide on what to do until I hear from some more folks here.

Thanks for the replies. Hopefully I will be able to resolve what it is I have. It actually runs sweet for about 5 minutes (in between cold and hot, when it gets too rich). I'll try and post a pic or 2 tonight.

Stuart
 
78 GS550 Wrong Carbs

78 GS550 Wrong Carbs

Well, after more research.

It looks like my bike has an engine made up from parts from both series engines.

I guess the 77/79 and 80/82 heads are the same, except that the carb boots and the boot mount bolt spacing are different between the CV carbs and VM carbs. I read that the CV series head has the bolt spacing wider, since the CV carb bores (venturi) are wider than the VM's.

I think I can assume the HEAD came from a CV engine (80-82) along with the CV intake boots and CV carbs. I'm now assuming that going back to VM carbs is not an option, since the head I have is already setup with CV carbs and CV sized boots. I hope someone now outbids me on Ebay for the VM's listed now.

The lower end has POINTS, which means 77-79 (I think).

The lower end has NO KICK STARTER, which should mean 80 - 82 or 79 - 82, I'm not sure. One place says the kick starter was on 79's , another place says kick starter was gone on 79's and later. I suppose someone could have put a 80 side cover without the kickstarter hole in the side on an older engine.

Anyway, I guess my question is answered? I have a GS550 mixed engine (may explain why ID is ground off) with points, no kick starter, but with a head that was MADE for CV carbs.

My path forward is to clean, adjust, and rejet the CV's.

Wish me luck. If anyone can tell me for sure I'm just out to lunch (i.e. you know that the heads are really the same), PLEASE tell me.

Stuart
 
Wrong Carbs, More Info

Wrong Carbs, More Info

Hi,
Well, I pulled the carbs last night. From the picture here (and the next ones). You can see I have the CV carbs. The next pix will show some details. As you can see from this pic, NO kickstarter. There are points under the crankshaft cover. I'm wondering if the airbox and airbox rubbers are the same size between the VM and CV carbed 550s?

Stu
 
Last edited:
More 78 GS550 Pix W/Carbs

More 78 GS550 Pix W/Carbs

Here are the Carbs. I'm ready to clean.

I did a bad thing. Even though I blocked and braced the float hinge posts, I broke one. Can this be brazed, soldered or epoxied?

My Jets:
Main: 92.5
Slow: 175
Pilot Air?: 40

Are these correct for a 80 GS550?

Stu
 
78 GS550 W/Carb Problems.

78 GS550 W/Carb Problems.

Here's the bike.

I paid $225 for it, and have spent $150 in parts (tank, signals, both switch clusters, entire speedo / tach / light cluster, clymer book).

If I can get the carbs right, mostly with labor, I'll have this bike roadworthy for around $400. And, its been a good bonding experience for my son and I.

Stu
 
WRong Carbs Update

WRong Carbs Update

I cleaned the carbs. They were dirtier than I thought. I couldn't say if I had a specific clog somewhere, but I cleaned, squirted solvent through, brass-wired, and blew out every hole, passage, jet, etc. There was some noticable rust around the pilot mixture screw (the little washer and the spring around the mixture screw). My mixture screw plugs were still in place.

My start/cold/choke circuit was clean. The passages were clean, and I didn't have a problem starting the bike anyway, but they got cleaned too.

I did the epoxy repair to the #3 carb float post. I think it will work. I set the float levels. Every float level was at 21mm. This seems way too low, causing a high fuel level. Could this be part of my over-rich problem? A post here says 22.4mm, and my clymer book says 26mm (or maybe I got that backwards). I set them at 23.5mm as a compromise. Since my bike was running very rich, maybe raising the float level (lowereing the level at which the float needle cuts fuel off) will help. I'm giving the epoxy repair a couple of days to fully cure.

Next, I'll put the carbs back on and test it. I know I have to check the mixture screws (1,2, and 4 were at 1-1/4 turns out, 3 was at 1-1/2). I set them all at 1-1/4. I'll also do a vacuum sync.

If I'm lucky, I'll be done, if not, I'll have to rejet. God, I hope not, but we'll see.

I have to ask this question one more time, since I've seen both answers.

Are the rubber boot-to-cylinder head attachments the same between the 77-79 VM carbs and 80-82 CV carbs? I know the carb diameters are different. I'm specifically asking about the bolt spacing where the boots attach to the head itself. A couple off pictures would help, if anyone has a closeup of the VM setup , and the CV setup.

Stu
 
If you have a pair of two-barrel carbs, then they're from a model that's newer than 82. The 80-82 GS550 models had 4 single-barrel Mikuni CV carbs.

-Ian
 
78 GS550 Wrong Carbs Update

78 GS550 Wrong Carbs Update

Finally got back to the carbs. I did a complete cleaning. They were dirtier than I originally thought. I pulled everything I could, including the mixture screws (I had to pull the plugs). I cleaned, gently poked (with a brass wire), and blew out every jet, orifice, and passage.

I repaired the float post that I broke off. I set the float level. They were all at about 21mm. This seemed too low (too much fuel in bowls), and didn't match my book or this site for the CV's. I set them to 24mm. I set the mixture screws to 1.25 turns. I did the "pre-synch" using the tie-wire trick off the XS11 site. #4 was pretty far off from #3. #1 and #2 were right on with #3.

I put it all back (Damn its a PITA with the stock airbox / boots), but couldn't get the airbox boots to stay on. They appear to be slightly too big in diameter. Maybe this is another 78 Airbox (should mate to VM Carbs) issue with my 80 CV carbs. I'm missing the clamping bands on the airbox side. I tried to use big tie-wraps, but #2 and #3 won't say on. I know I have to get this sealed before I try and do any more tuning.

I fired the bike up and it runs ALOT better. The richness and stumbling are gone. There is a bit of synch unbalance at idle and at the point when you just keep the throttle between open / closed while driving at road speeds.

Once I get the airbox boots sealed, I'll set the mixture screws, check my timing again (I only set it statically), and do a proper synch. Perhaps my plugs are fouled from the previous super-rich condition.

I'm getting close. I may go with pods because of the pain of pulling the carbs, but, then I'd have to buy the jet kit and start the jetting process. I'd rather just stay stock.

So, my 78 with CV carbs now actually runs. I'm a happy camper.

Anyone have the CV carb airbox side boot diameter?

Stu
 
Wrong Carbs Update

Wrong Carbs Update

Got the airbox side boots tightened. Helped the idle a little. I adjusted the mixture screws and re-did the timing (1-4 were a little advanced, 2-3 a little retarted, now right-on). Each tweak gets me a little closer.

My mixture screws are now at 7/8 to 1 turn open. I'm still a little rich. I replaced the plugs again, and I'm going to do a plug test to see at what RPMS the richness is worse.

I have good performance 1/3 to full throttle. I have a very little stumble from off-idle to accelleration.

I'm still having an idle problem. After running hard, If I come to a quick stop, the idle usually depresses about 200 to 400 RPM and the bike wants to stall. If I run the idle up a little, then about 1/3 the time, the idle creeps up too high after a run.

I'm at 6800 feet, so I may just be suffering from rich jetting. I'm pretty sure I've got all air leaks fixed. My filter is not clogged. The slight stumble just off-idle while accellerating, and the rich sparkplug indication are my last issues. I am going to back through and check all the ignition wiring, since I know it was messed with. Perhaps I have an intermittant spark issue because of poor harness connections. We'll see.

Stu
 
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