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hjacobmiller
Guest
Just a thought - wouldn't it also have bad vacuum if it had bad compression though?
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2BRacing
Forum Mentor
The intake stroke on a 4 stroke engine occurs when the piston moves down, and the inlet valve is open.
The compression stroke occurs when the piston moves up, with both inlet and exhaust valves closed. So "leaks" at valves or rings would result in low compression.
However, the rings would have to be really non-functional to result in a bad vacuum. Under such extreme conditions the compression would probably also be low. However, an engine at such an extreme stage would probably sound like a bucket of bolts rattling around!
Regarding your earlier post about feeling dumb, don't knock yourself! You are asking questions here and folk are giving replies in order to help you learn and increase your knowledge base. Only people who think they know everything and are afraid to ask, are the real dumb ones! I am probably a couple of times your age, but I have learned a heck of a lot about GS's on here, and I am still learning things every day!
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hjacobmiller
Guest
Well I went back and threw a set of compression gauges on now that I pulled my head outta my @$$.
The right cylinder held steady at 160 and left was the same.
Don't think I have any reason to worry about a burnt valve on either side do I?
The right cylinder held steady at 160 and left was the same.
Don't think I have any reason to worry about a burnt valve on either side do I?
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2BRacing
Forum Mentor
Good to have compression numbers as close as possible to each other across all cylinders, so all is in order there.
Now you need to sort out the vacuum gauges to get a proper carb synch. Check that the adaptors that screw into the inlet manifold tube seal properly. I use a tiny rubber o-ring on my adaptors to make sure they seal. Check that the hoses fit securely onto the adaptors. Check that the hoses fit securely onto the vacuum gauges. Make sure you have fitted the restrictors either in the vacuum hose or in the base of the gauges to damp the fluctuation of the gauge needles.
Warm up engine and try carb synch again. The actual numbers of the readings on the gauges does not really matter - as long as both cylinders are the same. The actual numbers will vary according to the revs anyway, so don't worry about the actual numbers. Just adjust the synch screw to get both readings the same.
Now you need to sort out the vacuum gauges to get a proper carb synch. Check that the adaptors that screw into the inlet manifold tube seal properly. I use a tiny rubber o-ring on my adaptors to make sure they seal. Check that the hoses fit securely onto the adaptors. Check that the hoses fit securely onto the vacuum gauges. Make sure you have fitted the restrictors either in the vacuum hose or in the base of the gauges to damp the fluctuation of the gauge needles.
Warm up engine and try carb synch again. The actual numbers of the readings on the gauges does not really matter - as long as both cylinders are the same. The actual numbers will vary according to the revs anyway, so don't worry about the actual numbers. Just adjust the synch screw to get both readings the same.
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hjacobmiller
Guest
I still can't get the carbs to sync. I must have a vacuum leak somewhere
I switched the hoses and still got low vacuum on the right side so I know it't not the gauges.
I also got a T and put both lines on one cylinder and the gauges pulled down the same.
I triple checked all of my connections between the gauges and the adaptors, had the tiny orings around the adaptors and also had the copper washer on the adaptor. I don't know where to go from here.
I'm wondering if I put the intake boots on upside down or something. I couldn't decide if there was an orientation of them or not, and I know the parts fiche lists different #'s for each side.
I adjusted the sync screw until I got it run as good as I could. I held my hand at the end of each muffler and seemed to be the same flow on each side. I know that really doesn't tell me anything but turning the screw definitely made it run like crap one way and better the other.
I checked all the boots to make sure the clamps were down tight, also cleaned and oiled the air cleaner, and tightened up the lid on the airbox.
The 300 doesn't have the same type of airbox as others so I don't know how to seal it up. I would also think that the vacuum would be low for both sides if it was leaking.
I did notice something though. There is an additional hose that goes back towards the airbox. From what I understand this is a hose that keeps pressure from building up in the carbs, correct? It isn't a vacuum line and I noticed the if I covered it it would stall the bike.
I switched the hoses and still got low vacuum on the right side so I know it't not the gauges.
I also got a T and put both lines on one cylinder and the gauges pulled down the same.
I triple checked all of my connections between the gauges and the adaptors, had the tiny orings around the adaptors and also had the copper washer on the adaptor. I don't know where to go from here.
I'm wondering if I put the intake boots on upside down or something. I couldn't decide if there was an orientation of them or not, and I know the parts fiche lists different #'s for each side.
I adjusted the sync screw until I got it run as good as I could. I held my hand at the end of each muffler and seemed to be the same flow on each side. I know that really doesn't tell me anything but turning the screw definitely made it run like crap one way and better the other.
I checked all the boots to make sure the clamps were down tight, also cleaned and oiled the air cleaner, and tightened up the lid on the airbox.
The 300 doesn't have the same type of airbox as others so I don't know how to seal it up. I would also think that the vacuum would be low for both sides if it was leaking.
I did notice something though. There is an additional hose that goes back towards the airbox. From what I understand this is a hose that keeps pressure from building up in the carbs, correct? It isn't a vacuum line and I noticed the if I covered it it would stall the bike.
