Continued Hard Starting Woes

[bill_face]

Hello everyone,

I'm trying to chase down a hard starting problem with my bike. I've had this problem for years and never got to the bottom of it. I've recently rebuilt the carbs (for a 2nd time) using an ultra-sonic cleaner and the officially recommended o-rings. I replaced the cylinder boot o-rings as well. It's now a lot better than it was but still takes a minute or so to start from cold. It takes a while to catch and when it does it turns over really slowly and keep conking out for a bit until it warms up. Then the choke eventually revs it up to about 3k rpm, If anyone has the patience to watch here is a video of me starting it from cold:

https://youtu.be/OP23rNoEqK8

In the near past, I have improved compression by having the head skimmed, checked valve clearances and changed the air filter. In the video above you see a starter battery connected to try and rule out my battery being a bit weak. The only other thing I can think to try is new spark plugs, but I've definitely tried that in the past. I've attached an image of the spark plugs after idling for some time while I experimented with the air screw settings. It looks like spark plug in chamber 2 has more carbon build up than the others and the one in chamber 4 has slightly less. 1-4 is right to left. Should I adjust for this on the fuel mixture screw or the air screws? In terms of the carb screw settings are all set the same at fuel screw 7/8th out and air screw 2 turns out.​

 

[Nessism]

When you cleaned the carburetors, did you verify that each choke pick up tube (brass tube that goes down into the float bowl) was open? Also, each passage in the float bowl? If any of these passages are blocked, you won't have choke in that carb.

Regarding the video, how long since the last start? Your bike acts like the float bowls were dry, and only started to fill while you were cranking. My old 1000S was the same way, because the prime feature on the petcock didn't work. You can check for fuel in the float bowl by draining the bowls as a trial. Catch the gas, and measure how much fuel is in each carb.

 

[bonanzadave]

I know your focus is on the carbs but don't overlook low voltage at the coils. Check it with a meter or just run a couple jumpers from the battery + to the coils.

 

[KiwiAlfa156]

I agree with Nessism, it sounds dry. Check the fuel tap is operating correctly. Try letting sit in the "PRIME" position for a minute and then give it crank. Report back. If my GS650 sits for more than a week or two, it needs to be primed.

 

[Steve]

I'll add one more thing that might need to be addressed: when was the last time you adjusted the valves?

As they wear, the clearances go tight. There is already precious little clearance, so any decrease starts hanging valves open (when cold), making for hard starts.

.

 

[bill_face]

Thanks guys. I did verify choke pickup passages were clear. Not sure exactly which passage you mean in the float bowl, but I remember there was a passage from the choke pick upp tube round into the float bowl and those were all clear. I was generally very methodical about checking everything was clear.

I checked valve clearances less than 300 miles ago, so I'll keep them at the back of the queue for now

That was 2 days since last start. I'll try the prime thing and draining the float bowls and see where that leads me.

Cheers

Phil

 

[dgates1]

My guess would also be the choke pickup path from the bottom of the bowl. I thought mine were clear until I hit them a second time with cleaner and compressed air. They were indeed NOT all clear. Page 51 on the tutorial from Ed.

Run an aux tank and try to start it to rule out the petcock. Also, you could use some new spark plugs.

https://gsarchive.bwringer.com/mtsac/~cliff/storage/gs/Mikuni_BS-CV_Carburetor_Rebuild_Tutorial.pdf

 

[Nessism]

Screenshot 2025-05-27 152327 by nessism, on Flickr

 

[Big T]

The choke pick up should start you bike immediately, so that's an issue

Another issue is your overly rich #2 spark plug. This indicates fuel is coming down the vacuum line into cylinder #2.
Unplug the vacuum line from the fuel tap, plug it and use Prime to run the bike

 

[jdub6092]

Sounds exactly like mine until I cleaned out the choke circuits even after three rounds of thorough cleaning, so my initial thoughts line up with others.

 

[bill_face]

Hey thanks all,

I'm definitely was able to spray carb cleaner through those choke passages. If I have the carbs off again I'll double check

I did some measuring of petrol and i think runnign dry seems like the main issue. Here are some weight's of petrol I was able to drain from the float bowls


Straight after ride

Carb 1: 30g

Carb2: 28g

Carb 3 27g

Carb 4 :26g

2 days after a ride

Carb 1 :20g

Carb 2: 21g

Carb 3: 15g

Carb 4: 12g

Starting with the bike in Prime helps tremendously. First time I tried it it started up within a few seconds. Then I did it again a couple of days later after having drained the carbs to do the above 2 day measurements and it started up straight away

I bought a new Petcock from Suzuki only a couple of years ago so I think that should be ok. Where is the petrol going?

In answer to another suggestion above the voltage across the coils is 10v. (see picture of where I took the measurement). I have done the coil relay mod and the voltage feeding the relay was 12.6V

​

 

[rphillips]

"Where is the petrol (gasoline over here) going"? That's a very good question I've wondered about for yrs. It happens quite regularly but usually takes a few weeks or months so just blamed it on evaporation. BUT, I never remember it happening within just a couple of days, that certainly can't be evaporation. Glad to see our pet cock is working properly, ON with no vacuum, no flow, on PRI pos. flow. Be glad you have the PRI to kind'f resolve your problem, my "83" Honda CB1100F has no PRI. after sitting a couple of months, the carbs are low of fuel. With no PRI I've got to engage the starter for a pretty long while to get vacuum to open the fuel valve, way too much abuse to the starter. Have learned if it don't start right up, fuel is low, use starting fluid to get it going to save the starter... If you find where the petrol is going, let us know.

 

[Nessism]

The fuel in the float bowls evaporates over time. The more heat in the carbs, the faster the evaporation.

The volume of gas in the carbs looks about right. You may want to experiment with using prime each time after the bike has sat for 2 days or longer.

 

[rphillips]

Agreed, the evaporation thing, it's the only option I've ever heard or imagined, relatively reasonably within a few weeks or months.... But evaporating roughly 50% of the volume within a couple of days, to me, seems quite unreasonable. No doubt if using the PRI helps noticeably, the gas is going someplace... Thinking, I don't remember you mentioning if there's a time frame till it gets hard to start. If you stop for gas then restart how does it start? If you ride it to work then restart 8 hrs. later how bout it? if you ride it today, then try to start it tomorrow how bout it? Just wondering if there's some sort of time frame when it noticeably harder? My opinion, usually 1 or 2 min. on PRI is good, but as it kind'f appeared on your video one carb filled first, slight ign., 2nd carb filled more ign., 3rd filled, more ign. then when all full running good. Different reasons some carbs may fill slower than others, give them 4 or 5 min. on PRI. just to be sure all are full..

 

[Alexander]

I'll try to give my little contribution, since the carburetors of my 1000G were in bad shape and I managed to put everything back as it should be.
After a season under the cover and without removing fuel or anything else, two laps and it started. When cold it suffers a bit, then after 10 minutes everything is normal.
You should try to disassemble the carburetors and put a direct fuel pipe excluding the tap, then disassemble the tanks and check the floats and their correct functioning. Mine had damaged pins that made the float get stuck, especially if tilted with the side stand, I replaced the pins and valves to fix them, the water line is important, if I remember correctly 12/13 mm. You have to put the air and fuel screws as per the manufacturer's instructions, mine was not present with the fuel one. Another problem I had was with the rubbers from the carburetor to the airbox, for mine they no longer exist and the ones I put in did not match, with the airbox, I put some silicone to remove air infiltrations, original filter and all the problems were solved, also take a look at the manifolds, they could take in air too.​ Also check the tank gaskets if they have the corresponding hole.