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Discussion Starter · #1 ·
Ok, took the bike apart over the wintter, polish and repaint everything. NEVER took the engine apart as there is only 13000 km's on it with no leak and compression. Got the carbs rebuilt by the local shop and put them back in.

The thing wasn't starting by its own before dismanteling, carbs were all gummed up, but would run putting fuel through the plugs.

The thing will not start now. New plugs with good spark and will run if put gas through the plugs. But nothing on its own and plugs were dry before putting fuel through the plugs.

Any advise?

Thx
 

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Sounds like no fuel in bowls. Take fuel line off and see if you have fuel coming out of fuel line. If you do, then put it back and try the drain screws at the bottom of the bowls. If you still have no fuel, your needle valves are most likely stuck/plugged.
 

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Discussion Starter · #3 ·
Fuel line is good and float bowls have fuel.

I have compression, spark, carbs rebuilt by local shop and have fuel in tank and float bowls, still no start. I put a new air filter and soaked it in oil before. Could it be the culprit? Took it off, but now the battery needs to be charged.

I'm at loss!
 

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Turn the mixture screws out 1.5 to 2 turns from the seated position.
When you turn the fuel on wait for 2 minutes before trying to start to give the float bowls plenty of time to fill.
 

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Discussion Starter · #5 ·
Ok, I will check with the local bike shop what they set the mixture screws at and go from there. Is it possible they didn't set the float bowl height properly and not enough fuel in the bowls?

Thx
 

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Discussion Starter · #6 · (Edited)
Talked to the shop and he said everything is set accordingly and no reason it would not start. He suggested to spray some propane in the intake to help it???!!! Maybe Starter Fluid instead.
 

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You should not need to use any starter fluid. Just the choke until it's warmed up.
Did you physically remove the float bowl drain screws and see fuel flowing out?
 

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Discussion Starter · #8 · (Edited)
Yes I did and fuel came out of both bowls. I have spark, compression is 145psi on both sides and have fuel in the bowls, but for what ever reason fuel doesn't go ( or suck from the cylinders) from bowls to the cylinders. It runs with fuel through the spark plug holes and with starter fluid, so timing isn't the issue here.

Local shop doesn't get it either and brought the carbs back to go through them again, as this is free and just time for me at this point. The shop guy said maybe the rings are stucked on the pistons and not enough suction. But all the rings on both pistons stucked equally, the odds are slim, no?

They say third time is a charm, right?

I'm hopping he will find something, otherwise, I'm at lost again. May have to bite the bullet and bring it to a guy that specializes in those kind of bikes in town.
 

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Discussion Starter · #9 · (Edited)
Ok, got the carbs back from the local shop and found nothing out of the ordinary. Everything is where it should be, he said.

He said play with it over the week-end to get something freed up, like rings stucked on the pistons. More starter fluid while running to get things warm and pray.

He is suggesting to get a compression leak test done at his shop: Pistons at top end, pressurize at 120psi through the spark plug holes and see if it looses more than 10%. If it does, it needs a top end job. If not, look at timing, advancer if it has one (don't know) and valve clearances.

Any suggestion? Anybody?

To summurize again: Have spark, compression is 145 psi cold on both (that's why rings stucked on both pistons at the same time and same place to get same compression, should buy lottery tikets), have fuel in the bowls and runs with starter fluid and gas through spark plug holes (tells me the timing is not the issue here). Fuel is not sucked from carbs to the cylinders for what ever reason.

Did I buy a money pit?

Thought it was a nice bike, nice project to work on and now that it is done, the dam thing won't start! Looks good though, isn't it?
 

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So it'll start and run on starter fluid. That indicates that the idle passages are plugged. Here's a picture of those where you can see the Red line indicating fuel flow
Carbcut.jpg
 

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Timing is basically fixed by the woodruff key on the crankshaft to rotor. There have been cases where that has been sheared off and it is possible to put the rotor on incorrectly and push the key out of the crank. If it was running before and you did nothing to the rotor then I don't see either of the 2 possibles happening. You can check the basic rotor position by using a straw thru the sparkplug hole and turn the engine until the piston is at TDC, then the rotor should be on the T mark at the pointer on the case. If that's good and you have spark then the timing is good. Advance is handled electronically thru the CDI. There's a sticky in the SOHC Electrical section on diagnosing the ignition system on these models.
 

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Does the choke really work??? Mine will not start cold without the choke on.
 

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Discussion Starter · #14 ·
I initially cleaned the carbs and change the jets, but decided to get it done by the local bike shop after I didn't set the floats height. He said there are tubes I didn't clean and now remember I could not get fluid going through the hole where the primary jet goes in both carbs. He took the emulsion tubes out and cleaned them. That is the only thing I could think of and he cleaned them.

Will put the carbs back on and get more starter fluid in.
 

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Discussion Starter · #15 ·
Well, no LUCK!

Everything is telling me a top end job. Ran for quite a while with starter fluid, enough to smell the fresh paint cooking on the engine. But there is no fuel going to the cylinders from the bowls and the carbs have been checked and rechecked by the local bike shop. I thought 145 psi would be enough to suck that fuel in. I have seen videos of a guy yanking the back wheel to get the engine unseized and than the thing would fire up without cleaning the carbs or on another post a cb 400 fired up with 125 psi. NOT MINE!

May have to get the compression leak check by the bike shop to confirm before hand.
 

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My CB400T started after being left out behind the barn for 15 years, compression about 150.
What should the compression be??? I cleaned the carbs and she ran, not really good but she ran.
A GM coil mod got her running like she should.
 

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Discussion Starter · #19 ·
I read a bite about it, but doesn't explain why it doesn't start though
 

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You have enough compression to start and run, 145 isn't great since spec is 185 but it'll start and run. Next up is spark and timing. You say there's spark already but is it at the right time? Have you checked rotor position like I posted earlier? The GM coil mod improves the spark, stock coil produced @15K brand new but of time that's decreased. GM coils are 50K volts so you get a hotter spark, most common results of this mod are easier starting and smoother idle. I'd suggest that you go thru the Ignition diagnosis sticky in the Electrical section to ensure that the ignition system is good. http://www.hondatwins.net/forums/64...400-450-cb450sc-manual-trans-1978-1986-a.html
The only thing left after the compression, spark and timing is fuel. This means that you will need to go thru the carbs one more time and I'd recommend that you read this before hand. http://www.hondatwins.net/forums/63-fuel-supply-carburation/24191-rebuilding-vbulletin-carbs.html
 
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