No Start after New Diaphragms

[TripleKing]

As my slides would stick until warm and my diaphragms had the consistency of wet noodles, I installed brand new genuine Suzuki diaphragms in my 89 Kat 750 carbs. Now she won't start. I am getting fuel to the carbs and I am getting spark. In fact, she almost catches from time to time, but she will not run. I checked schematics and a youtube video and I seem to have everything right. Am I missing something? Is there an issue with replacement diaphragms? Please help me.


I have fuel in the lines and I have spark. This is driving me nuts.

[Kreylyn]

As my slides would stick until warm and my diaphragms had the consistency of wet noodles, I installed brand new genuine Suzuki diaphragms in my 89 Kat 750 carbs. Now she won't start. I am getting fuel to the carbs and I am getting spark. In fact, she almost catches from time to time, but she will not run. I checked schematics and a youtube video and I seem to have everything right. Am I missing something? Is there an issue with replacement diaphragms? Please help me.

I know, I know... you been messing with the carbs so that is your focus atm, but follow me here a second....




What's the voltage at the coils on the bike? Measure key on, and when the starter is turning the motor over.


If your under 11v at any time, then your going to have start issues.


It's a simple thing to check before going further, but it's a major cause of hard cold starts.


Krey

[TripleKing]

I'll check the voltage, but spark seems good and it started easily and normally immediately prior to my changing the diaphragms.


Voltage checks out.

I know, I know... you been messing with the carbs so that is your focus atm, but follow me here a second....




What's the voltage at the coils on the bike? Measure key on, and when the starter is turning the motor over.


If your under 11v at any time, then your going to have start issues.


It's a simple thing to check before going further, but it's a major cause of hard cold starts.


Krey

[TripleKing]

It was down to 1/4 tank. I added about a gallon to get to half a tank. Now if you cranks it for about 10 to 15 seconds it will let a LOUD backfire out of the right pipe. It would even start to catch. It just goes BOOM. This is frustrating because it ran fine (except for a little slide sticking/ diaphragm issue after sitting for a few days. Now, she just goes boom!

[TripleKing]

After fire is a lean condition. Your carbs are clogged. Probably happened when you removed the tank, you stirred the sediment in the tank or your petcock isn't functioning correctly.

I was thinking petcock, but it is flowing. Maybe carbs are clogged, but I doubt it was it they were really clean when I had the tops off and it started perfectly the other day. I guess I have to pull the carbs. I was trying to avoid that as it is a pain on Kats and I just had them synched in March. Also, I rolled it down a hill in my development. I got it up to about 15 and put it in second. It would not even come close to firing, even when I opened the throttle.


Also, when I crank it a bit, you can really smell fuel, like it is flooding. This happens even when the choke is off. I think I am getting all the fuel I need. Maybe too much.


Oh, one other thing. I get the backfire when the battery is the strongest. After the battery loses a little power from cranking, I will get a little stumble as it tries to catch, but no backfire. When I say backfire, I mean a shotgun blast with fairly thick smoke wafting from the right pipe.

[Kreylyn]

I was thinking petcock, but it is flowing. Maybe carbs are clogged, but I doubt it was it they were really clean when I had the tops off and it started perfectly the other day. I guess I have to pull the carbs. I was trying to avoid that as it is a pain on Kats and I just had them synched in March. Also, I rolled it down a hill in my development. I got it up to about 15 and put it in second. It would not even come close to firing, even when I opened the throttle.


Also, when I crank it a bit, you can really smell fuel, like it is flooding. This happens even when the choke is off. I think I am getting all the fuel I need. Maybe too much.


Oh, one other thing. I get the backfire when the battery is the strongest. After the battery loses a little power from cranking, I will get a little stumble as it tries to catch, but no backfire. When I say backfire, I mean a shotgun blast with fairly thick smoke wafting from the right pipe.

Double check the plugs are correct. left coil with white wire 1 -4, right coils with black wire /yellow stripe is 2-3. Out of order or swapping the wires will = no run or bad run/backfire.


So your getting 11+ volts even when the starter is turning the motor over, and the battery passed a basic load test? Hrm... okay, moving on.


Are you trying to start the bike with the airbox fully on and properly attached, all the clamps are tight for example?


All the vacuum caps are plugged off and you have the vacuum line for the petcock attached to the petcock or plugged off?


Petcock works? Fuel is flowing? You used prime and the bowls are confirmed full?


Krey

[TripleKing]

Double check the plugs are correct. left coil with white wire 1 -4, right coils with black wire /yellow stripe is 2-3. Out of order or swapping the wires will = no run or bad run/backfire.


So your getting 11+ volts even when the starter is turning the motor over, and the battery passed a basic load test? Hrm... okay, moving on.


Are you trying to start the bike with the airbox fully on and properly attached, all the clamps are tight for example?


All the vacuum caps are plugged off and you have the vacuum line for the petcock attached to the petcock or plugged off?


Petcock works? Fuel is flowing? You used prime and the bowls are confirmed full?


Krey

Plug wires are just as they were when it ran fine Thursday nigh, Carbs were never off the bike. I am over 11 volts even wen cranking. Battery is only a few months old, full charged and cranks strong. Vacuum line is attached to petcock and carbs. I am getting vacuum. I have fuel in the bowls and have tied prime. Like I said, if I keep cranking, it smells like the carbs eventually flood. Choke is operable, other than taking the fuel lines and vacuum line off of the tank, no other lines have been touched.


I have no clue why it started very easily Thursday, but will barely get a little bit of a stumbling fire or backfire today. When I say stumble, I do not mean a stumbling idle. I mean I can hear the cylinders try to fire. If I crank for 10 seconds I might get an attempted fire. I might get a backfire from the right side, but it is not even close to ticking over. Also, it seems to do "best" when the choke is set 1/4 lean from full rich. At full rich or less than 3/4 closed to fully open, it will do nothing.


All clamps are tight and I cannot find any leaks. Tank was cleaned last year so there should not be much floating around in there. I could under stand if one or even two carbs were clogged, but no cylinder tries to fire.


All I did was change the damn diaphragms!


In frustration, I walked over to my 1970 CB450 project which I have not started in a week. The old girl with the original unopened engine fired right up. Grr!

P.S. Sometimes it seems like it wants to start then boom! I don't want to keep trying because I hate the noise.

[Kreylyn]

Plug wires are just as they were when it ran fine Thursday nigh, Carbs were never off the bike. I am over 11 volts even wen cranking. Battery is only a few months old, full charged and cranks strong. Vacuum line is attached to petcock and carbs. I am getting vacuum. I have fuel in the bowls and have tied prime. Like I said, if I keep cranking, it smells like the carbs eventually flood. Choke is operable, other than taking the fuel lines and vacuum line off of the tank, no other lines have been touched.


I have no clue why it started very easily Thursday, but will barely get a little bit of a stumbling fire or backfire today. When I say stumble, I do not mean a stumbling idle. I mean I can hear the cylinders try to fire. If I crank for 10 seconds I might get an attempted fire. I might get a backfire from the right side, but it is not even close to ticking over. Also, it seems to do "best" when the choke is set 1/4 lean from full rich. At full rich or less than 3/4 closed to fully open, it will do nothing.


All clamps are tight and I cannot find any leaks. Tank was cleaned last year so there should not be much floating around in there. I could under stand if one or even two carbs were clogged, but no cylinder tries to fire.


All I did was change the damn diaphragms!


In frustration, I walked over to my 1970 CB450 project which I have not started in a week. The old girl with the original unopened engine fired right up. Grr!

P.S. Sometimes it seems like it wants to start then boom! I don't want to keep trying because I hate the noise.

Plugs are clean? Possible they have been flooded or fouled with the other issues?


Krey

[TripleKing]

Plugs are clean? Possible they have been flooded or fouled with the other issues?


Krey

I pulled them once and they looked fine, not fouled. I have just about given up. I don.t even want to work on it because of it booming out the right pipe. It is not a backfire lime a pop, but a blast. The concussion actually shook a box of cotton swabs off a shelf 6 feet away.

Lets get down to basics. I took the old diaphragm off and installed a new on the slide. While doing so I took out the spring and jet needle. I reinstalled the needle by putting the little plastic spacer on the bottom and the little hat on the top of the needle. The the spring and then the top with the covered port lining up with the hole on top of the carburetor on the engine side. If I did anything wrong, that is where it would be.

The only thing I can think of is that the new diagrams are stiffer than he old ones and are helping to keep the slides and the jet needle closed more so.

[92xjunker]

The diaphragms have absolutely nothing to do with your starting issues. I told you what the problem was. Try draining the carb bowls to remove any crap in the carbs. Your not running fuel filters right?

[arsenic]

the diaphragms have absolutely nothing to do with your starting issues.

+1,000

[TripleKing]

Right, I'll pull the bowls, but it will be a waste of time as the tank was cleaned over the winter. I have fuel going into the engine. In fact, if I keep cranking it will flood. Works best when choke 3/4 closed or, as it got warmer, half closed. Almost fired a few times today. I had a shop synch and clean the carbs in March. Except for the "sticking" after it sat for a few days (never acted up when driven every day) the bike ran and started normally right up until I changed the diaphragms. I drained my tank and looked with a flash light, the darn thing is spotless.

It has to be something I did or did not do when reinstalling the diaphragms and slides. This is not project bike which has not been running. It gets used three to five times a week. The gas does not get old. When I opened the carbs to change the diaphragms I was amazed how clean they were. They looked like they came out of the box. If anything I am getting too much fuel, not to little.

My backfire is a popping back fire from running too lean. It is raw fuel exploding in the right pipe (but never in the left). I thought it might be spark because another time when I had that happen my battery was weak.

All I know is that it ran before the new diaphragms and it does not now. The diaphragms might not make a difference, but if the slides, needles springs or carb tops are not right, they could make a difference. Trouble is that I have checked and rechecked.

I have dealt with clogged carbs before, but none were ever like this. I have dealt with very lean carbs which would pop and backfire at low speeds, but this actually has an explosion in the exhaust pipe. I have witnesses who swear it is igniting in the muffler or close to it.

[92xjunker]

Check that the needles are installed into the correct hole and not hung up. Lift the slide with your finger to check that, no need to disassemble. Try starting then immediately pull and inspect the plugs for fuel.

[TripleKing]

Check that the needles are installed into the correct hole and not hung up. Lift the slide with your finger to check that, no need to disassemble. Try starting then immediately pull and inspect the plugs for fuel.

Slides are right. Almost started last night when I got home from dinner. Decided to let the battery charge. Will try again today.

[TripleKing]

Check that the needles are installed into the correct hole and not hung up. Lift the slide with your finger to check that, no need to disassemble. Try starting then immediately pull and inspect the plugs for fuel.

I cleaned the plugs (again, as they got a little wet from cranking) and installed to old diaphragms and after a few stumbles she struggled to life, but only briefly. I tried to restart and she stumbles a few times and then belched flame about a foot long out the right pipe. Scared the heck out of my nearly 20 year old son.


She is getting plenty of fuel. There is not lean condition here. What is happening is she is loading up on fuel and raw fuel is igniting in the pipe. I will say that she was much better with the old diaphrams in. I know they are not supposed to make a difference, but...




So here is my theory. The new diaphragms are holding the slides more closed than the old one. This means the carbs were not getting enough air via the idle circuit, but the slides were making up for it. It is also possible that I am installing the springs wrong. For the record, I have, in order from bottom to top, the round spacer on the needles, the e-clip (which I have not touched) then the little "hat" top to the needle. I pout that down the center hole in the slide until it bottoms and then installed the spring on top of that until it is free and resting on top of the needle. I the put the carb top on with the spring attached to the "tab" in the center of the carb top.


If there is anything wrong, it is the air intake for the idle circuit or I have something wrong with mu install. Man, I love slide carbs versus CV any day.