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Discussion Starter #1 (Edited)
Hi all!


I got a Suzuki gs450L 1987

I had to take my cilinder off to do some work. When putting it back together I put the timing bolt on RT and checked if the right cilinder was on top. I put my valves cams back on with the #1 aligned horizontally with the head. Put the valve chain back on. Counted 18 steps, starting from #2 to the other cog wheel’s #3 marker. Everything was put back together but when I try to run the engine it has problems running the pistons up and down. It feels like it has way to much resitance and I could feel my wires getting hot. When I remove the sparks it goes smoother.

Any ideas on what I did wrong?

Cheers,
Daan
 

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Trying to understand this :/ so is the resistance you are concerned over engine compression ? and the compression goes away when you remove the spark plugs? because yes that makes perfect sense.

Wires getting hot :/ you lost me there, Plug wires or other? ... I can't say I've ever grabbed a spark plug wire to see how hot it is, with my luck I'd get a heck of a good shock.

Now lets assume you have put the engine back together and the valve timing is close enough that you are not crashing the pistons into the valves. If I wanted to know if everything was functioning like a 4-stroke motor should, I would do a compression test and for that you don't even need to start the motor, just turn it over a few strokes.

Hope that helps some, how far off am I from understanding the problem?
 

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Discussion Starter #3
Thanks for the reply TrialsRider!

So I dont know much about engines..

I'll try to clear it up a bit:
with the spark plugs IN, and trying to electric start the engine, the pistons only go up and down once every second or so (which seems way to slow to me?).
When doing this for let's say 6s I could see one small black wire giving a little fume of smoke, like almost melting. Thats when I felt the rest of the 'wiring bundles' and they were all getting pretty warm.
When removing the spark plugs the pistons go up and down faster. Not sure if that means anything :/

If you say to test the compression I could turn the engine over a few strokes, how do I know the compression is ok?

Is it perhaps possible that there is an electrical problem or wouldn't the starter engine even run in that case?

Thanks a lot!
 

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Ok, electrical wiring getting smoking hot is not a good thing, you have a short circuit somewhere and for some reason your fuse did not blow. That is scary.

A 4 stroke motor is just like a big air compressor, to do a compression test you remove a spark plug, bung a dial gauge compression tester into the plug hole and turn the engine over. The compression tester has a dial gauge that tell you how many pounds per square inch of compression your engine is producing on its compression stroke ... probably in the vicinity of ~180 pounds.
(or whatever your service manual says) if your valves are not right your compression will not be right so right away you would know you have a problem.

In a 4-stoke motor your crankshaft (pistons) go up and down at twice the rate of your cam shaft.

As for how fast does the starter need to turn the motor over to start it? <- idle speed. If you can't spin the motor up to idle speed it probably won't start.
 

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If you had the head off you need to adjust your valve clearances and you can't do that until your cam timing is correct, valve clearance is set at TDC (Top Dead Centre) which is the correct term to describe when the piston is at the top of its travel.

For compression TDC your intake valves have just completed closing and the piston is on its way up to TDC. Just a couple degrees before that your spark plug fires the fuel/air mixture.
Don't accidentally set your valve clearances on the next TDC stroke, which is right after the exhaust valves closes and the intake valve starts to open.
... is a 4-stroke motor so the crank turns over twice for each time it goes bang, it is the compression stroke TDC where you set the valve clearance not the one following that.
 

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Discussion Starter #6 (Edited)
I checked this tutorial to set the timing right:

When I align the #1 marker arrow with the cilinder head, the left cilinder cam lobe is already pushing one valve down, which makes the cam shaft not just fall in its place. That's not supposed to be like that right?
 

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The marks for the cylinder you are setting the timing by would logically indicate TDC, at TDC none of the valves on that cylinder should be open, so ya it sounds like your valve timing is not right.
Just be careful you don't set it so the valves collide with a piston :/ that would be devastating.

... must confess I did not watch the video yet, I usually just go by the service manual. Do you have a copy of the OEM service manual?
 

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Discussion Starter #8 (Edited)
I do not have a service manual unfortunately but on all the videos I've seen they explain it exactly the same but it seems like it doesn't match with my cam shafts for some reason :confused:

So maybe this explains it better: (screenshot from video above)
Here he can align #1 on the cam shaft with the top of the head but when i do that i have to really push the cam shaft down in its place because one of the cam lobe (X on screenshot) is already facing downwards, or is that supposed to be like that?

Group 2.png
 

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Not sure I can get my head around it without seeing it :I need to relate the position of the cam lobes with the start of the power stroke on each cylinder,
at #1 TDC, the #2 cylinder is at BDC. Either it has just completed the intake stroke and the intake valve has now completely closed,
or just finished a power stoke and the the exhaust valve is just starting to open to open, because we know the crank shaft is staggered 180 degrees, correct?
So if my brain can think in 2 cylinders all your valves are now closed, I think something is wrong, when #1 is at TDC #2 should have both valves closed.
Would be real nice if somebody could proof read that for me!

... no way you could have mixed up the intake and exhaust cams or cam parts is there, or is that impossible ?
 

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Discussion Starter #11
I managed to get him to run again! First I checked in the cilinders with a flashlight if the valves were popping in and out at the right times, which they did. After that I put some oil in the cilinders and gave it some turns which made him run but only when putting some fuel directly IN the cilinders. he seems to not pull in fuel on his own.. I did change to K&N pod filters instead of the airbox and just ordered a main jet size of 137.5. What other reason could cause it not to pull in fuel on his own? Hope it's ok to change the issue here :)
 

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Is your thread, do whatever you want!

Don't go chasing carburetor jet sizes thinking that will make the difference of sucking fuel or not, it don't work that way, your engine draws in fuel and air mix as the result of the vacuum that is produced during the intake stroke of the piston.

The carburetor is little more then a toilet tank (that's your float bowl) and a spray bottle (that's the part that atomizes the correct amount of fuel into the intake path) if your motor is producing vacuum at the correct time (intake valve timing) then one of those other 2 things is still a problem.
 

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When you had the carbs off the bike did you plug the intakes with a cloth and when you reinstall the cards forget to take them out? Seen that a few times over the past couple years the people in a rush to get their bikes up and running and leaving them in
 

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Discussion Starter #14
@scramblermike I took the cloths out, would have been funny tho hehe
@trialsrider apparently they do suggest to change the main jet after switching to pod filters from an airbox? and 137.5 should be a good size to get they say?
maybe cleaning my carbs out could fix this issue.. i'll keep you guys posted!
Thanks again
 

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Good, hurry up I want to see pictures of it jumping over shit. :cool:

oh wait, you probably don't jump over shit with that bike, I just want to see it ...
what are you going to do with it again? do you do wheelies?
 

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Discussion Starter #17
Good, hurry up I want to see pictures of it jumping over shit. :cool:

oh wait, you probably don't jump over shit with that bike, I just want to see it ...
what are you going to do with it again? do you do wheelies?
Hi guys, I started working on the bike again last weekend. I cleaned out the carbs and mounted my nice pair of k&n filters on it. Still when trying to start it now it doesn't run without the choke. Apparently this means my pilot/idle jet is clogged but I'm sure I cleaned that jet and the whole passage with some compressed air.. Is there another reason why this could be happening? Pilot jet is unchanged from the standard, main jet is 137.5 now.

Cheerios!
 

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Hi guys, I started working on the bike again last weekend. I cleaned out the carbs and mounted my nice pair of k&n filters on it. Still when trying to start it now it doesn't run without the choke. Apparently this means my pilot/idle jet is clogged but I'm sure I cleaned that jet and the whole passage with some compressed air.. Is there another reason why this could be happening? Pilot jet is unchanged from the standard, main jet is 137.5 now.

Cheerios!
I found a copy of the owner manual, that says there is only 2 things you can set on the carburetor, idle and throttle cable slack.
Found a writeup on cleaning those POS CV carbs: GS450_Carb_Rebuild_Guide

Symptom you described suggests a plugged pilot jet. ... you have 2 carbs,
is there anything such as heat coming off the motor or out both exhausts to confirm that it is operating on both cylinders but carburating equally poorly?

Odds of that are slim unless you are not cleaning either of them sufficiently. There are a slew of videos out there on the subject,
here is one picked at relative random, is not great but not bad either. https://www.howtomotorcyclerepair.com/onlyrunsonchoke/
in the video he has the advantage of only 1 carb to deal with.


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nice pair of k&n filters on it"
Pod filters? no airbox? no velocity stacks? no intake plenum? Still trying to make that work on constant velocity carburetors and a free flow exhaust?
:/ you are probably still spinning your wheels, I doubt it has ever been made to work well given those parameters. Your vacuum operated carburetors might not even be moving the slides yet if it is running only on the choke circuit.

When it is running on the choke I assume only at idle and you slowly apply some throttle, what happens?
 
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