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What next? Colortune or Sync Carbs?

  • Thread starter Thread starter robgusto
  • Start date Start date
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robgusto

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I have an 81 GS750 straight pipes 2 into 1 times two, with pods. I have rebuilt the carbs per the link on Bike Cliff's webpage (good info couldn't have done it without ), I then rejetted with a DynoJet stage 3 and adjusted the floats to 22mm. I bought K&N Pods to replace the cheap pods that came on bike. I have an aftermarket (non vacuum type) petcock installed that came on bike from prev. owner. I have a Colortune on order and can't wait to see how it works. That's the history now for the challenges... I am leaking gas out of the first carb through the filter, I have a high idol even after adjusting the idol knob all the way to low and I did check for hangups on the cable, my #3 cylinder is not firing/cold pipe. I pulled the #3 plug and it was soaked in gas. All other plugs are carbon fouled, running rich. The question is where to start? I have a friend that can help tune the carbs and I will have a Colortune this week. I still have the gas leak at the air filter possibly due to rejetting? I don't want to call Dynojet unitl I have a chance to run the bike to get more info, and I don't want to do that until I get cylinder 3 firing. Everything looks good from the coil (visual inspection of wires) and Compression test (cold) is 120, 122, 122, 121. Any ideas on where to start?

Also, thanks to those who have helped me so far!! I started working on the bike two months ago. This forum and Bike Cliff's website have given me a lot of great info/confidence to take on a new hobby!!
 
robgusto said:
I have an 81 GS750 straight pipes 2 into 1 times two, with pods. I have rebuilt the carbs per the link on Bike Cliff's webpage (good info couldn't have done it without ), I then rejetted with a DynoJet stage 3 and adjusted the floats to 22mm. I bought K&N Pods to replace the cheap pods that came on bike. I have an aftermarket (non vacuum type) petcock installed that came on bike from prev. owner. I have a Colortune on order and can't wait to see how it works. That's the history now for the challenges... I am leaking gas out of the first carb through the filter, I have a high idol even after adjusting the idol knob all the way to low and I did check for hangups on the cable, my #3 cylinder is not firing/cold pipe. I pulled the #3 plug and it was soaked in gas. All other plugs are carbon fouled, running rich. The question is where to start? I have a friend that can help tune the carbs and I will have a Colortune this week. I still have the gas leak at the air filter possibly due to rejetting? I don't want to call Dynojet unitl I have a chance to run the bike to get more info, and I don't want to do that until I get cylinder 3 firing. Everything looks good from the coil (visual inspection of wires) and Compression test (cold) is 120, 122, 122, 121. Any ideas on where to start?

Also, thanks to those who have helped me so far!! I started working on the bike two months ago. This forum and Bike Cliff's website have given me a lot of great info/confidence to take on a new hobby!!
Click to expand...


If you haven't already you need to synch the carbs. The high idle most likely is that one of the slides is out of synch.

You said you're using a non-vacuum petcock. What did you do to the carb fitting for the petcock connection? It should be blocked, otherwise you'd have a vacuum leak and may also cause it to idle high.

The fuel leak suggests that there is a float needle not fully seating. Usually it's due to some debris preventing the needle from making full contact with the seat.

Make sure the float height is being measured from the correct position. Sometimes the measurement is taken with the gasket in place other times without.
 
Okay I will be synching carbs on monday when my friend comes over with his tools. As far as the carb fitting it has been blocked with a cap. I will recheck the float height tomorrow afternoon. I don't think I have a leak but from what I have been reading I think I should replace the intake boots just to be sure. Any suggestions on the best place to get them affordably? Also I did notice that the cap that blocks the vacuum for where the old petcock line used to go is getting old. It is not letting any air in but I may want to replace. Since it's not an original bike part does anyone have any ideas about where to pick one up?
 
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You can get the boots from the stealership, but I would call Z1Enterprises (315-926-5054). They can get a lot more things than they list on their site and are a lot more helpful than the stealership. And you have to fix all the leaks before you can move forward.
I got caps at my local NAPA store.
 
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Thanks for the heads up on the boots I will call Z1 enterprises on Monday. I just inspected the boots and they look good and are not leaking but they are slightly aged so I will pick up a new set.
I just got done adjusting the float height and I'm not leaking gas anymore!!! When I tipped the 3rd Carb over the float seemed to be stuck? I also have a much better/lower idol now. Next is sync and colortune. I let the bike idol for 5 min and the 3rd pipe is still just warm not hot. I'm sure the Colortune will at least let me know if there is spark and I can further troubleshoot from there.
 
Spark, Compression, Fuel, but no go on cylinder 3

Spark, Compression, Fuel, but no go on cylinder 3

I got the Colortune and was excited to give it a try. I wanted to start with the 3rd cylinder because it's the one I suspected had no spark. I hooded it up and I had spark? I tested compression to find they were all very close and had good compression on every cylinder. Also I know the carb is delivering fuel because the spark plug is wet when I pulled it. So I have spark, compression, and fuel but the pipe is still relatively cold and fuel is coming out the exhaust??????? My only guess is there is something wrong with the carb even though it is set up like the other 3. I have rebulit/rejetted/and re taken apart and inspected all 4 carbs. Any ideas?
 
robgusto said:
I got the Colortune and was excited to give it a try. I wanted to start with the 3rd cylinder because it's the one I suspected had no spark. I hooded it up and I had spark? I tested compression to find they were all very close and had good compression on every cylinder. Also I know the carb is delivering fuel because the spark plug is wet when I pulled it. So I have spark, compression, and fuel but the pipe is still relatively cold and fuel is coming out the exhaust??????? My only guess is there is something wrong with the carb even though it is set up like the other 3. I have rebulit/rejetted/and re taken apart and inspected all 4 carbs. Any ideas?
Click to expand...

Try swapping the #2 and #3 spak plug wires and see if the problem goes away. If the problem follows the plug wire i would replace the coil.

You mentioned a sticky float valve. Did you correct that problem?
 
Okay just swapped 2 and 3 and the same thing. Let run for 5 min and felt pipes the 3rd pipe was still cold. So it's not the coil, good idea though at least I can rule that out. As far as the float goes, after I adjusted them I did fix the sticking problem.
 
When you get the intake boots from Z1 make sure you replace the boot "O" rings as well, this area is always a culprit for air leaks.
 
I found a set of carbs on ebay bidding starts at $120 shipped. I would only need the 3rd carb and I will have to rejet that carb but I'm running out of options. I am only guessing it's a carb issue!!! What can I check in the engine to see if there might be a problem internally? The compression is good and spark is there so what could it be? I am stumped?
 
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Perhaps I missed it but I dont recall any mention of new plugs?

You say number three is getting fuel but have ya tried loosening the drain screw to see that there actually is fuel in the bowl?
 
The plugs were replaced aprox 3 weeks ago. I swapped plugs to see if it was an individual plug problem as well and still nothing on cylinder 3 so I have ruled out the plugs. There is fuel in the bowl, the plug is also wet so it's definitly getting fuel.
 
I have pulled the carbs off again and inspected the jets and float, nothing out of the ordinary. I also pulled the #3 plug and looked in the cylinder to see if it was wet. Nothing out of the ordinary except for the plug dripping wet with fuel. I'm almost to the point of buying a new carb if I can find one, even though I can find nothing wrong with the current one. Anyone know any places to try to get a rebuilt carb other than ebay?
 
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