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Bought a motorcycle....

  • Thread starter Thread starter Suzukizilla
  • Start date Start date
S

Suzukizilla

Guest
but wound up with a flame trougher.

Ok seriously now... tried to start the 750 this past weekend. Cranks fine, got nice blue spark but wont start. After cranking for about 5~10 seconds it finally goes off like a cannon shooting a foot long flame out the back. I'm now a hit with the neighborhood kids who seem to think this is cool but not exactly what I bought my GS for. I dont have the air cleaner box on (which from reading around may or may not be an issue) because its missing what looks like a foam seal on the top part of the filter. I have an idea on how to fix this but will wait to see if it works before posting results. Also I need to ask about the fire order, is it 1-4 from left to right sitting on the bike? Also do I need to plug/run hoses from the vaccume ports on the carb (again reading around found thats what they are) becaue there is no hose going to the tank? I currently have the tank off the bike connected to the carbs with a long gas hose. I've had the carbs off and checked each bowl. There was some funk but cleaned up pretty easly. I did the test with spraying a little starting fluid in each cylinder and it ran for a second when the carbs were off. Oh and another FYI it has a 4 into 1 exhaust with no baffle. Also can somone tell me what size the stock jets are? Well thats about where I'm at for now :confused: TIA.
 
You have two coils on this bike and each coil fires two cylinders. The coils actually fire every rotation of the crank so that each cylinder gets a spark on the compression stroke, and a spark on the exhaust stroke - which is basically a wasted spark. Normally, cylinders 1 and 4 are on one coil and cylinders 2 and 3 are on the other.

I would check to see if you have a couple of the sparkplug wires crossed to the wrong plugs.

Hap
 
Hap Call said:
You have two coils on this bike and each coil fires two cylinders. The coils actually fire every rotation of the crank so that each cylinder gets a spark on the compression stroke, and a spark on the exhaust stroke - which is basically a wasted spark. Normally, cylinders 1 and 4 are on one coil and cylinders 2 and 3 are on the other.

I would check to see if you have a couple of the sparkplug wires crossed to the wrong plugs.

Hap
Click to expand...

Yep the wires on the coils are numbered and I know the firing orded is 1,2,3,4 but is that left to right or right to left (sitting on the bike)?
 
The center vacuum port of the three needs to be hooked to the petcock, or plugged. That might be why it won't fire. The outer two are vents. With your mods, you can leave them as is without hooking hoses to them. The cylinder order is 1-4, left to right sitting on the bike. Stock main jets are 102's for the 750. With your pipe, you might need to re-jet if it hasn't been done already.
 
Suzukizilla said:
Yep the wires on the coils are numbered and I know the firing orded is 1,2,3,4 but is that left to right or right to left (sitting on the bike)?
Click to expand...

Sitting on the bike the cylinders are numbered, left to right, 1, 2, 3, 4. I'm not sure the firing order is 1-2-3-4 though...I don't think it is. It may be 1-4-3-2. Need to check the shop manual to be sure.

Hap
 
firing order is 1-3-4-2, this is by far the most common firing order for a in-line 4 cylinder engine.

the outside (1-4) pistons move up and down together, and the inside pair (2-3) move together, so for even firing intervals you only have two choices of firing order. 1-3-4-2, and 1-2-4-3, for some reason I am not aware of, 1-3-4-2 is far and away the most popular, I am not aware of any engines that use 1243.
 
Last edited:
also, four cylinder engines only fire two cylinders each revolution.
 
focus frenzy said:
also, four cylinder engines only fire two cylinders each revolution.
Click to expand...

I guess what I ment is the cylinder numbers from left to right 8-[ but it looks like I had the wires on right.

renobruce said:
The center vacuum port of the three needs to be hooked to the petcock, or plugged. That might be why it won't fire. The outer two are vents. With your mods, you can leave them as is without hooking hoses to them. The cylinder order is 1-4, left to right sitting on the bike. Stock main jets are 102's for the 750. With your pipe, you might need to re-jet if it hasn't been done already.
Click to expand...

The center port had a hose jumped from center to the left one so I'm just going to plug the center one and also see what size jets I have.
 
looks like you have a yoshimura 4 into 1 exhaust on that bike, can you please take a couple pics of your carbs and post them, just want to check if they are stocks carbs or another type.

the vacume port you have read about would be located on the front side of the carburators (the side in between the carbs and the motor) and is typically smaller then the other ones, for now if you have one plug it so no air can flow through it. the other port on the far left and far right are vent ports, they can be left open. the middle port is the fuel port need i say more.

you said you removed the gunk from the carbs, did you follow the carb clean series posted, step by step or did you just spary around a little bit. this is important in determining if your carbs are pluged up or just got things hooked up wrong.

-ryan
 
first timer said:
looks like you have a yoshimura 4 into 1 exhaust on that bike, can you please take a couple pics of your carbs and post them, just want to check if they are stocks carbs or another type.

the vacume port you have read about would be located on the front side of the carburators (the side in between the carbs and the motor) and is typically smaller then the other ones, for now if you have one plug it so no air can flow through it. the other port on the far left and far right are vent ports, they can be left open. the middle port is the fuel port need i say more.

you said you removed the gunk from the carbs, did you follow the carb clean series posted, step by step or did you just spary around a little bit. this is important in determining if your carbs are pluged up or just got things hooked up wrong.

-ryan
Click to expand...

Think the carbs are stock Mikunis as it has MIK I think stamped in the side but I'll get picks or a serial number tonight.

I'll have to relook at that vac port. because it looked like it was facing slightly toward the rear of the carb (of coarse not the gas inlet) just above the middle of the carb.

Basicly I just sprayed around and took a wiretie and dug around some of the ports to see if there was anything in them which there wasnt. I know I'll have to soak these carbs but I was just seeing if I could get this thing to run so I can get an idea of what I'm dealing with. Also taking things kinda slow cause I hurt my shoulder about a week ago and have limited use of my right arm.
 
first timer said:
the vacume port you have read about would be located on the front side of the carburators (the side in between the carbs and the motor) and is typically smaller then the other ones, for now if you have one plug it so no air can flow through it. the other port on the far left and far right are vent ports, they can be left open. the middle port is the fuel port need i say more. ryan
Click to expand...

If they are the stock carbs (like shown in the pic), the ports face toward the rear... toward the air filters. Hook-up is as I stated earlier.

100_1655.jpg
 
Thats them. Hey Reno where does that braded line run to? Mine just has a hose that loops from the two outlets (out one side into the other). Is it for some kind of oil cooler?
 
focus frenzy said:
1-3-4-2 is far and away the most popular, I am not aware of any engines that use 1243.
Click to expand...

I used to agree with you, at least until I read through my clymer manuals for my 650 AND my 850.

I was very surprised to see that BOTH of them have a 1-2-4-3 firing order. :shock:
 
Alright I think I know what the problem is and it might have to do with the airbox. 1st I checked the plugs again and realizes that the plugs were gapped too wide so I fixed that. Then as I was pulling the plugs I realized that even after all this cranking they are bone dry. So I remembered an old trick to put your hand over the back of the carb to create suction and low and beholed there was a backfire in that cylinder. So I pull the plug and it drowing in gas. So do I need to get the airbox fixed or is the carbs so gummed up that its just not pulling gas from the bowl?
 
It lives... for a few seconds anyway.
Put the air filter back in the airbox, got the box back on the bike but I have to pull the choke up as far as I can get it to keep it running for maybe 20 seconds then it just dies. Sometimes with a backfire. Sounds like its loading up (flooding)and killing the motor. Cold and choked it will idle @800 rpm. When it starts warming up (choked)it will idle @1200 but as I said it will slowly bog and die. So what now?
 
Guess I need to clean the carbs like First Timer said and see where that gets me. Unless anyone else as any ideas?
 
That would be a good place to start. Take those carbs off and clean 'em up. I would also get the orings for your carbs from www.cycleorings.com
Robert Barr (a member).
 
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