New owner here with Carb issues

[602busa]

Hey guys, I just picked up a 1979 Gs750 project that looks less like a project and more like a cafe racer, pics to come. But I'm having a problem. The guy before did some non repairable work to the stock carbs. Needless to say I bought a set on ebay, the performance kind. The problem is that the manual says I need a size 42 spigot flange to the intake side of the carb since my stock boots don't fit. Does anyone know where I can find a set of these? All my searches seem to come up empty or unclear. If I can't find some soon I'll just have to go back to a stock carb if anyone has one for sale.

Here is the carb I bought: https://ebay.to/2n8vKVM

 

[scratch]

Those are probably overkill for your bike... that's "overcarburation".
You are probably a world better off sorting your stock carbs.
There are probably 1/2 dozen guys on this forum who would rebuild your old carbs and get you sorted for a lot less dough and trouble...

I know that is not what you are asking but, what you are asking is for directions down a path that doesn't make much sense and I'm just looking out for my 2-wheeled kinfolk.

 

[602busa]

No I actually appreciate that. the carbs I have on the bike are completely not reparable. So i only have 2 options, go back to stock, which I'm ok with, or attempt to adapt these carbs to the bike. do you know of any available carbs? What do you mean by over-carburation? Are these carbs over-kill?

 

[scratch]

Well for starters, finding the intakes that match... #2 the bore size is signifigantly larger than stock... they could work and be tunned but, IMO it's a bit of overkill for a driver street bike unless you have a built motor with more fueling needs... Others may disagree, someone may chime in and contradict me & I may learn a thing or two.

Stock makes more sense, the chain of fittment items, tuning, streetability, expence etc...

I'd look for a used set of Stock VM carbs that are complete and don't have any obvious defects such as broken posts, stuck slides, hacked bowl tubes or what not.
Ebay has a couple of decent candidates for $180-250
Clean and rebuild with new o-rings and gaskets... $35
I assume that the fuel mixture screws are broken on any used set of VM carbs, maybe you get lucky but I usually account for another $25-50 for mixture screws and misc replacements on average. Since you have your old carbs they may have any misc parts you need.

If you rebuild them yourself, that's about half the cost of the new flatside carbs alone The resources and tutorials to do the work are here and readily available. If you are going to own a vintage bike, the knowledge gained by doing your own rebuild will be well worth the effort.

If you post in the parts wanted forum, another member may have a good set to sell as well... Your old carbs may be salvageable or tradeable to ofset some of these expenses...

Lastly, how about a picture of the carbs you have showing the damage? Just for kicks, I'm currious to see how bad they are...

 

[Guest]

What he means by "over-carburetion" is that those carburetors are probably too big for that stock engine. You can adapt them and they will probably run but you will most likely end up with really poor fuel mileage, bad throttle response and poor fuel/air mixing; making them hard to tune properly.

I would also suggest to start with some stock carbs unless you plan to modify the engine. They can be had for a fairly reasonable cost from someone modifying their bike and they come up on Ebay pretty regularly. Stock would be VM26's. KZ1000 carburetors will also work with a couple minor differences, they can sometimes be had cheaper although they won't be "correct".

Just out of curiosity what damage was done to your stockers?

 

[602busa]

I'm not sure exactly whats been damaged but I'll find out this coming monday. This is coming straight from a mechanic that has the bike in the shop, I've just done a complete overhaul on it and this is the last bit to get it complete. He is saying that the drilled large holes into the carb in an attmept to make it run differently. Not much to go on and I'll be going into the shop to confirm exactly what the damage was, but the guy before me had a Harley exhaust put on the bike and attempted to mod his carbs to work with that exhaust. If you can point me to link of some decent looking carbs I'll have a look. I'm really ready to end this project lol. by the way, what do you think of these: https://ebay.to/2LV7k0D

 

[Guest]

That set looks to be complete and he mentions in the description that the slides are not stuck. Another thing to look for are cracked overflow tubes in the bowls. I'd be a little suspicious about why 2 of the float bowls look worse than the others. Otherwise it may be a good buy.

I think it goes without saying that they will need at least new O-rings. Everyone here seems to use cycleorings.com, the kit is cheap and make sure to replace the intake O-rings while you're there

 

[602busa]

I like this one better: https://ebay.to/2O8pCbx

But I'm not sure if a 1983 carb will fit a 1979 bike. Any thoughts?

 

[scratch]

I'm not sure exactly whats been damaged but I'll find out this coming monday. This is coming straight from a mechanic that has the bike in the shop, I've just done a complete overhaul on it and this is the last bit to get it complete. He is saying that the drilled large holes into the carb in an attmept to make it run differently. Not much to go on and I'll be going into the shop to confirm exactly what the damage was, but the guy before me had a Harley exhaust put on the bike and attempted to mod his carbs to work with that exhaust. If you can point me to link of some decent looking carbs I'll have a look. I'm really ready to end this project lol. by the way, what do you think of these: https://ebay.to/2LV7k0D

So the mechanic butchered them worse... From the hands of one butcher to another... Ok, in the best interest of your wallet, let's see what horror has transpired before getting spendy. Perhaps it is only the slides that were drilled.
Harley mufflers did not change the jetting on my friend's 550 once they were attached correctly and leaks at the couplings addressed. Does it have the orriginal head pipes (is it a 4 into 2 set-up or 4 into 1? Cant tell from the photo). The orriginal owner may have been trying to correct other issues with re-jetting? (ignition, timing, valves out of spec, air leaks, carbs dirty or out of tune)

What else has the mechanic done?

The carbs you have linked to are the correct ones and they do appear to be serviceable but... hold tight till you see what the story is with yours eh?

I like this one better: https://ebay.to/2O8pCbx

But I'm not sure if a 1983 carb will fit a 1979 bike. Any thoughts?

Those are not correct, different type of carb for a different motor. You are looking for carbs from 1977-1979, the "VM" type like the first set you linked too. But again, hang tight till you see what happened to the orriginal carbs. Is the mechanic going to pay for replacements as far as the damage that was done?

 

[602busa]

So far the mechanic has just inspected the carb and tried to get it running correctly. He told me the carbs were in bad shape and it would be best to buy new. Again I'll find out on monday the exact situation with the carbs and get more details. But yes I'll wait till I hear more before I buy more. I have no problem buying them to be honest.

 

[Guest]

+1 for waiting to see what you have, I should have thought about what you said before. I can't really see anyone drilling holes in anything other than the jets or slides. If that's the case they can be saved.

I know from experience a lot of "mechanics" that may work on old cars prefer to buy new carburetors rather than rebuild. It makes sense with those where you can buy a brand new carburetor for $100 and be good to go. Sometimes you can end up with more problems than solutions trying to buy a new set for these things

That being said Scratch is totally correct that the ignition and valve clearances should be well sorted before starting on the carbs

On a side note, I'm not sure if moderators can move posts on TheGSResources but this would be more suited to the Carb/Fuel/Exhaust section (Where there are many people that know much more than I do)

 

[Spyder]

Ok, just a thought, a scenario if you will. I don't know if you know the mechanic or not... There aren't too many mechanics in the industry anymore that know how to properly setup, and tune a set of 4 carburetors... Without saying, "I can't get these to run right" (therefor don't have to pay him for that work) he tells you that these are shot, and you need new ones. NOW he can charge you double the R&R labor, PLUS double the tune cost... NEVER trust a mechanic. ALWAYS trust your own eyes... My advice, go get your bike, and handle these carbs yourself. You just might need a new set of carbs, or not... You really won't know until you get them, inspect them, and let THESE guys see what you have going on...

 

[scratch]

I have no problem buying them to be honest.

It's refreshing to hear someone who is willing to open the wallet to get a bike problem sorted...

 

[602busa]

Ok, just a thought, a scenario if you will. I don't know if you know the mechanic or not... There aren't too many mechanics in the industry anymore that know how to properly setup, and tune a set of 4 carburetors... Without saying, "I can't get these to run right" (therefor don't have to pay him for that work) he tells you that these are shot, and you need new ones. NOW he can charge you double the R&R labor, PLUS double the tune cost... NEVER trust a mechanic. ALWAYS trust your own eyes... My advice, go get your bike, and handle these carbs yourself. You just might need a new set of carbs, or not... You really won't know until you get them, inspect them, and let THESE guys see what you have going on...

I agree 100%. I went down to check myself what was going on this morning. He explained it pretty clearly what the issue was. The guy that I bought the bike from wasn't quite as forthcoming. So the mechanic says the fuel mix screw was drilled into in an attempt to tune the harley pipes. Also there are small holes in the slide that came about due to the hacking from the previous guys handiwork. He also drilled into the body of the carb so there is no seal now. So i went ahead and ordered this: https://ebay.to/2LZnOVs However, I was leaving to take the RS carbs I bought back and asked him if he knew of a place that carries the boots I need if I decided to use the RS carbs. He mentioned a company called www.sudco.com. I called them up, the guy I spoke too was very good. I told him what I was trying to do, and he says "ya we don't carry GS750 intake boots to fit an RS carb, but the KZ1000 boots will mount right up. You just need to ream out the mounting holes maybe about 2mm and they will mount right up to the carbs no problem. $63 later and they should be at my front door in 2 days. I really want to see how it runs with the RS carbs since I already paid for them. I have until next week to return them so that should give my mechanic enough time to install and test them. I have the carbs with me now so the minute they arrive I'll test fit them first. If not, I'll just rebuild the stock ones. I'll keep you posted. Thanks again for listening and all the help so far.

 

[602busa]

It's refreshing to hear someone who is willing to open the wallet to get a bike problem sorted...

I'm a firm believer in that if I can't afford to fix, I shouldn't own it.

 

[602busa]

I do handle some of my own carb work. I just finished rebuilding my DR650 carb and I just got lazy I guess. Not only that when I brought the bike into the shop it had a host of other problems... allow me to list.

Random leaks in several places on the engine = Complete Gasket Kit $68
Worn sprocket shaft seal = $11
Rear brake rebuild was needed = $50
Fork tubes were bent = Used fork tubes $149
Rear tire rotted out from age = $135
Ignition coils were corroded = New Hi Perf Coil set $68
Exhaust was leaking = New Exhaust from Delkevic $335
Rust in the gas tank = Tank expoxied and new petcock = $375

I just didn't have the time to do all that, fortunately I had the funds lol. Now the last thing that's giving me trouble are these carbs. Hopefully the boots I bought will work out and I can put this to bed.

 

[Guest]

If you really want to give the RS carbs a shot, they can be made to work.

That being said I can't find anything wrong with the picture of the carbs you posted. Maybe I'm blind but I've looked a couple times and don't see anything.

One more thing is that I'd really be interested to hear how the Delkevic exhaust sounds, I have an unknown brand drag pipe on my 78' that scrapes every time I try to turn right. I had a delkevic on my CB350F and loved it

 

[Rich82GS750TZ]

One more thing is that I'd really be interested to hear how the Delkevic exhaust sounds

https://www.youtube.com/watch?v=Zh8C69g4wQs

 

[602busa]

If you really want to give the RS carbs a shot, they can be made to work.

That being said I can't find anything wrong with the picture of the carbs you posted. Maybe I'm blind but I've looked a couple times and don't see anything.

I really do, I can tell this to anyone else thats trying to do this that the stock airbox will not fit with RS carbs. I'm going to have pods installed. I'll post a video up soon to let you know how it works out.