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Discussion Starter · #1 ·
I recently purchased a 1980 Honda CM400A.

When I bought it from the guy it couldn't start on its own without starting fluid so when i got it and took it home I decided to strip the carb down and clean everything and rebuilt it.

Tried to start the bike and it just turns and turns with or without choke added and the petcock is on and clear of any obstruction along with the fuel line and a new air filter, and new gas. Starting fluid is the only thing keeping it started but when it warms up you can keep it on for at most 20 seconds once warm and just dies.

Messed with the idle screw initially to see if there is a change and got nothing then set the dl screw back to a base setting and moving onto fuel air mixture screw and looked up that it should be 1 1/2 to 2 turns out.

Doing a compression test tomorrow to see if there might be an issue in that department but for now the issue remains unknown.
 

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It does run but only on a starting aid spray ?

I presume there is fuel flow from the tank to the carbs, and fuel is in the float chambers, at the correct fuel hieght ?

I assume there are no air leaks between carb and engine ?

Does it have any compression at all ?

Come back after checking above and compression test.

I assume plugs, HT, timings and valve clearances are correct ?

Get a pair of those inexpensive HT checkers, the red neon plug caps, make an adapter so they fit inline with the oe plug caps. They flash when HT passed thru them. A cheap and effective visual aid for checking purposes, well worth the money.
 

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Discussion Starter · #3 ·
It does run but only on a starting aid spray ?

I presume there is fuel flow from the tank to the carbs, and fuel is in the float chambers, at the correct fuel hieght ?

I assume there are no air leaks between carb and engine ?

Does it have any compression at all ?

Come back after checking above and compression test.

I assume plugs, HT, timings and valve clearances are correct ?

Get a pair of those inexpensive HT checkers, the red neon plug caps, make an adapter so they fit inline with the oe plug caps. They flash when HT passed thru them. A cheap and effective visual aid for checking purposes, well worth the money.
It only starts with starting fluid and wont continue running without the aid of more spray.

They are at the correct fuel height.

Very possible there could be an air leak between the carbs and engine.

Does have compression both cylinders are at 150 psi exact for each.

Plug clearance is correct haven't checked for valve clearance or timings and no need for the ht checkers as both spark plugs produce sufficient spark.
 

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You cant change the timing it is controlled by the CDI. I dont think its in the ing. Are the plugs wet after you try to start it? .Remove the gas cap. I dont think its pulling a vac in the tank but try it any way. Are the float valves working ? In your opening you stated the petcock and fuel lines are open turn the petcock open then open the carb drains and see if gas runs out the drain tubes .If your getting gas in the carbs it should run . Maybe not very well but should run. Dont try to adjust the valves till you hear it run you my not need to. Sounds to me like you need to pull the carbs and rebuild them.

Just my thoughts

Bill H
 

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Discussion Starter · #5 ·
To start off the carbs were rebuilt recently, the plugs are we after attempting to start. Gas runs out of the tubes even when not running. i'll try the gas cap thing either today or tomorrow when i can get around to it.
 

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If the gas is running out of the tubes when not running the floats are to high or the float valve seat isnt stopping the flow of fuel when the bowl is full. Are your plugs wet after trying to start the motor. If the gas is running out of the carbs the tank doesnt have a vac problem. If the plugs are wet your flooding out the motor. If the plugs are dry then you might have fuel in the bowl but its not getting to the motor.

Bill H
 

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Discussion Starter · #7 ·
If the gas is running out of the tubes when not running the floats are to high or the float valve seat isnt stopping the flow of fuel when the bowl is full. Are your plugs wet after trying to start the motor. If the gas is running out of the carbs the tank doesnt have a vac problem. If the plugs are wet your flooding out the motor. If the plugs are dry then you might have fuel in the bowl but its not getting to the motor.

Bill H
It starts now the float height was the issue. Thanks for the help
 
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