Maybe time for intake boots

[Guest]

Ok, I think it maybe time for intake boots for my 1978 GS750. Having rebuilt the carbs last year I have recently got the bike running somewhat decent. This weekend I had problems getting it to start from cold. It would almost catch but not quite fire up so I had to resort to starting fluid. Once warm it seemed fine.

I took it out and it was very powerful, almost as if nothing was wrong. So, I took it home and started making small adjustments to the fuel screw in the bottom of the carb. It was out 3/4 of a turn from seated do I adjusted them up to 2 turns and nothing. When cold would not start......

I started it with starting fluid again, got it warmed up and tried to adjust the air mixture screws, currently set at 1 turn out. This had little effect on the motor, even with all 4 screwed all the way in. I was expecting the engine to stall out with them all in but it did not. So, with it idling I sprayed brake cleaner at the intake boots and it caused the engine to almost stall. When I sprayed at multiple boots at the same time the engine did stall.

That was as far as I had got so this coming weekend I will be removing the carbs and taking a look to see if the boots were tightly clamped to the carbs and the head. The rubber 'O' rings between the boots and the head were replaced at the time of the carb rebuild so I don't expect them to be a problem unless they weren't properly seated when installed. Again, this will be subject to investigation this weekend. I was really hoping the boots were going to be ok but if they are not them the only alternative is to replace........ We'll see what happens on the weekend and take it from there.

Am I missing anything here ?

Jamie

[Griffyn]

Sounds like you definitely have an air leak somewhere. But before you reach for that can of ether again, try adjusting your valves.

As someone who's been almost exactly there recently, valves solved the hard start and boots solved the idle.

[mvalenti]

Sounds like you definitely have an air leak somewhere. But before you reach for that can of ether again, try adjusting your valves.

As someone who's been almost exactly there recently, valves solved the hard start and boots solved the idle.

+1 on the valves, and the boots may be fine are they soft or hard n crunchy? You might just need orings replaced.

[Jamie]

I checked the valves already, all are between .06 and .09mm except 1 at .04mm. That one will get changed out to .09 in the coming weeks.

The O rings were replaced already so unless one or more got pinched and are not in the groove properly when I installed them then I think the boots are toast. I have no idea on the history of the boots, they could be the original 1978 boots for all I know. When I looked at them they didn't seem too pliable but I've never really seen a new pair so I have nothing to gauge them by.

I will take them off next weekend, check the O rings and see if I can see a problem with the boots (cracks, hardened, etc).

This site is fantastic, reading through the posts and using the search function has yielded so much information. Thanks guys

Jamie

[Jamie]

Well I found 1 of the clamps loose that clamps the boots around the carbs. Tightened it up and it started right up on the choke. Ran good and after warming up I again sprayed brake clean at the boots and this time nothing. It carried on idling just the same, not even the slightest change.

After warming up I took it out for a ride and it ran great. It pulls hard all the way to the red line. Everything seems fine now.

Jamie