GS450 Cafe Project

[pat_in_the_hat]

Alright. So I finished my first bike project 2 years ago. It is a '75 xs650 hardtail. I ride it almost everyday, and im completely happy with it.

And now I feel like I have too much free time and would like to do another project, a cafe. I spotted a '81 suzuki GS450 for sale on facebook for $100.

Curiosity got the better of me and I went to check it out. Its in pretty rough shape and has been thru alot. The owner said it was running great last winter, but he starting tearing it down to do a cafe project. He said he just really wanted to get it out of the garage and that I could have it for $50. So I bought it. It needs alot of love. Plus, i found out it doesnt have a title, so I need to get that sorted out. Quick question, from looking at the tank, its the 450L model, correct?
My main concerns so far are the hack job the PO did to the tail. For some reason he cut off the upper rear suspension bolts and welded them to the front of the vertical frame bar.

And the bolts on the engine side covers seem to be pretty stripped out. Any ideas/hints on how to get these loose without stripping them more?

So far, my plan is to get it put back together and make sure it will run. Then I will make some changes. My "goal" is to make something similiar to this xs750. Probably with the same paint scheme even...

 

[pat_in_the_hat]

ok. so need a little help.
I havent been able to spend much time on this bike. But i have been able to clean alot of the dirt/grime off, stripped down the wiring and rewire it with a temporary system just to get it running and charging. Cleaned the carbs. And I have been trying to get it started.

BUT. when I turn it over, it doesnt fire. It has compression of 100 and 105, enough to get it running, right? Ive grounded the plugs to the motor and seen a healthy spark, Ive given the carbs a good clean. Ive just been pouring fuel into the fuel line where it would connect to the tank (no tank for now). That should still work right, it doesnt need a higher back pressure from fluid in the tank? And the battery turns the motor over, so the battery shouldnt be the problem.

Ive sprayed a squirt of starting fluid into the back of the carb. But it backfired once, sent a decent flame out of the exhaust and a flame back out of the carb.

To me, it seems to be missing fuel, is there something im missing about these bs34 carbs? Some little trick? i dont have the vacuum conection plugged since im not using the petcock/tank right now, but that shouldnt matter, right?

 

[DohcBikes]

Yes, the vacuum port on your vacuuum operated carburetors needs to be plugged to ensure proper operation.

Have you checked the ignition timing?

Have you checked the valve clearances?

Have you checked the float levels?

Best to use a temporary container for fueling, because yes the extra pressure does theoretically help fill the carbs with gas, but I don't think that's your issue.

 

[DohcBikes]

ok. so need a little help.
I havent been able to spend much time on this bike. But i have been able to clean alot of the dirt/grime off, stripped down the wiring and rewire it with a temporary system just to get it running and charging. Cleaned the carbs. And I have been trying to get it started.

BUT. when I turn it over, it doesnt fire. It has compression of 100 and 105, enough to get it running, right? Ive grounded the plugs to the motor and seen a healthy spark, Ive given the carbs a good clean. Ive just been pouring fuel into the fuel line where it would connect to the tank (no tank for now). That should still work right, it doesnt need a higher back pressure from fluid in the tank? And the battery turns the motor over, so the battery shouldnt be the problem.

Ive sprayed a squirt of starting fluid into the back of the carb. But it backfired once, sent a decent flame out of the exhaust and a flame back out of the carb.

To me, it seems to be missing fuel, is there something im missing about these bs34 carbs? Some little trick? i dont have the vacuum conection plugged since im not using the petcock/tank right now, but that shouldnt matter, right?

also know that these carbs are not really going to want to work at all with no plenum on them. A combination of direct vacuum loss from an open port and no contained air charge on deck can be enough to make them unable to supply the correct amount of air and fuel to run the bike.

And yes 100psi is low. That isnt helping. This could be a result of tight valves, which can also cause backfiring.

also, you say "sprayed a squirt of starting fluid into the back of the carb. But it backfired once, sent a decent flame out of the exhaust and a flame back out of the carb"

There are 2 carbs. If your gonna spray starting fluid into it to try and get it running, spray it into both.

 

[pat_in_the_hat]

also know that these carbs are not really going to want to work at all with no plenum on them. A combination of direct vacuum loss from an open port and no contained air charge on deck can be enough to make them unable to supply the correct amount of air and fuel to run the bike.

And yes 100psi is low. That isnt helping. This could be a result of tight valves, which can also cause backfiring.

also, you say "sprayed a squirt of starting fluid into the back of the carb. But it backfired once, sent a decent flame out of the exhaust and a flame back out of the carb"

There are 2 carbs. If your gonna spray starting fluid into it to try and get it running, spray it into both.

alright, thanks for the help. Im guessing the plenum youre referring to is an air filter box or pod? Would that make a big enough difference that it wouldnt fire? And yea, I was going to spray starter fluid in both carbs but it backfired before I got to the second (I only have 2 hands). Ill check the clearances this week if I get time. But it should still fire if the timing is off right? Just would run like shit? Or am i wrong there

 

[DohcBikes]

Check those things and go from there.

Air box and plenum can be synonymous but not always. The point is to have a comensurate volume of contained air and the correct size inlet that keeps the pressure and velocity maximized and stable. You can mock up a tuneable airbox and use it as a tool to find out what works best for your application.

Pods are just filters, and your carbs do not perform correctly or to their potential with pods. Anyone suggesting otherwise is dreaming.

Read my post carefully. These suggestions are possibilities, not guarantees. It is much more difficult to diagnose a problem over the internet, so the person asking needs to realize that he/she is going to have to put their hands on the bike and check/change things, and report the results accordingly, or we will all be left chasing our tails.

Check the ignition timing, cam timing, gas level, and valve lash. Report results.

Thanks.

 

[Erskine]

Welcome. I like your XS build.
If you have the old air box I'd throw it back on for now.
CV carbs are finicky buggers and are fussy about how they have their air delivered.
Getting them to run right without a reservoir of still air is a dark art that I do not pretend to understand.

 

[hillsy]

Are you sure you have the coils the right way round?

 

[pat_in_the_hat]

thanks everyone for the help! I do not have the stock airbox. The po had a sheet of filter like material zip tied to the back of the carb. really ghetto. But he said it ran great like that. And yes, I know you cant trust what the po says.

hillsy, I wish it were the case, but my coils are connected right and on the correct cylinder. That would be a very easy fix...

Ive been reading in a cymer manual that the '80+ gs450s have an electronic ingition system and are "preset and nonadjustable". Is this correct?



please forgive me for my ignorance ha... Im trying to learn

 

[Erskine]

If the sidecover screws are chewed up, do the head and other engine bolts show signs of removal .... ie has the engine been torn down? Eliminating mechanical possibilities really points back to fuelling then.

Hill billy next step is to put a teaspoon of petrol down each plug hole and see if that gets it firing. I've started a few stubborn engines with this method.

 

[hillsy]

If you take off the RHS cover over the crankshaft you will see the ignition pick-ups. They should be electronic and non-adjustable.


It will take 5 seconds to swap the plug leads over and eliminate the possibility of the coils being wired incorrectly (the backfire out of the carb and exhaust suggests you may have them wrong).


Also, you need a more positive source of fuel than just pouring some down the fuel line.


This, at least.....