Motorcycle Repair / My Suzuki GS 450 L
Expert: jon ovington – 12/15/2007
I have a 1981 Suzuki gs 450, and I am having trouble hooking up the vacuum hose from the petcock. I know that the 2 brass pipes on the inner part of each carb is for air, but I am not sure where to plug the vacuum to. And also, when I start it, and it is running for a few minutes, if I even touch the throttle or the choke, it dies. Itll start back up, but it dies.
What do you think that would be? Thank you very much
Hi Clint, i am in truth not too familiar with your bike, and there were a few different variations depending on year/month, and country, as to exactly what spec it is. However, as to the vacuum pipe, i had a look at the fiche for one of the carbs for an 82, the reckoning behind that btw is that the 81 fiche didn’t show a carb, and I would assume that the carb fitted to the 82 would be pretty much the same, there are two variations at this address though, have a look at a grat resource here, http://www.cmsnl.com/suzuki-gs450-1982-sz_model13446/partslist/FIG17.html
if you see in front of the main part of the carb, closest to the intake flange, I see a vertical tube inlet, that would seem to be a good bet, there really can’t be many more options. Has it ever been attached?
The length of the pipe will surely give you a probable destination, taking into account any obvious bends in it’s route that the rubber pipe wants to take, (memory in the plastics world, I believe) As to the running problem, that could be down to a few things, assuming the vacuum tube isn’t playing a part in it’s stalling. Which it may well do. common to a lot of similar questions, but first, has anything been altered recently, tweaked, or replaced, change in use, climate etc.
Just to give you a pointer in to where you might look initially. The most obvious is the mixture of the fuel/air in to the engine. Once warmed and popped into gear, you say the motor will cut out, or die, when the mixture is too rich, i.e. too much fuel to air ratio this can happen.
Now there are a few things in a carb that might cause that, check out the air filters, and seals between carbs and engine, any leaks around the seals will cause the ratios to alter in a big way, and a clogged up air filter, will of course restrict the air intake, and subsequently the mixture will enrichen take the carbs apart, for a thorough clean, if the bike has been lieing a while, old fuel can break down it’s constituents and gum up the small airways and the jets. New fuels only have a shelf life of 3 months tops, check the float level with the spec in the manual, if you don’t have a manual, the spec will be online somewhere. reset to correct height if necessary.
Also, check out the jets and airways in the carb, check the jet sizes, number stamped on jet, to the spec in the manual. Bear in mind that different locations can have different affects on the carb settings to performance. For instance, different altitudes, and different climates make a difference, and also weather conditions, now in the colder months, in the northern hemisphere anyway, certain carb settings may not work as well as they did in summer months.
Now that is much of the carb/fuel side, you then have the ignition side of things to contemplate. BTW as i wrote before, if you feel that a particular area is at fault, and/or recent work was going on there, check that area first, you probably don’t want to sit down strip the carbs clean and put them on to find a loose wire in the ignition side that was causing the problem all along.
Anyway, When an engine starts and idles that is one thing, OK but then when a load is applied, this can cause an increase on the draw from the ignition components, and if there is any breakdown of insulation in the system, or a component that is capable of working during lower revs, but gives up as soon as more revs are asked for, the increase in amperage may cause failure. Check first of all your wiring to the coils, to the cdi unit, to the stators, check in particular the HT leads, are they brittle and old, check the plugs and the plug caps, or in america, the boots.
Have a look at your spark, remove, connect to HT lead, earth against engine, by touching the metal body of the plug to the metal part of the engine, please don’t hold it! or you will light up. Crank the engine a bit to observe spark with ignition on of course. You want a nice fat blue spark, a weak white yellow spark indicates less than satisfactory conditions.
It would start the bike, but as more fuel mixture is pushed into the cylinders, the increase in pressures and explosion will cause the spark to fail, it is a very hostile environment during the ignition sequence of an internal combustion engine as you can imagine, it needs to be a fat good spark. Even if there is a good spark, it may be disappearing during normal running, which would at first point you to a coil, again there are test parameters for your coils in the manual, it tests the resistance by ohms, through both the primary and the secondary circuits.
Maybe you have a tester, or can borrow one, to be honest they are handy things to have around, and aren’t expensive. If so far everything checks out, you would be moving on to the cdi unit, which can only really be swapped out with a known good one as they are usually sealed, and not adjustable. However, to tell you the truth, I would suspect that your fault lies in some of the aforementioned, and you won’t get as far as the cdi unit, they are quite robust after all.
As i said, Check the easy things first, the ignition connections, the overall condition of the plug, cap, HT leads, low tension leads etc.
test the coils, nice and easy, then move on to the carbs, check through potential leakage, blockage air filters etc. then move into the carbs for good clean and check jetting and float heights.
It could be anything I have touched on, however, I think you will find your answers in the fuel side rather than ignition, but you never know until it’s all checked
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