Checking Carbs

[Finley]

93 225TLRR
I 've been chasing a miss at idle. Really not a miss but a cyl not firing or receiving fuel. Compression is OK. I'm getting spark on all 6 cyl. Pumping the fuel blub does not help. It pumps up tight. All fuel bowls have fuel.
I have removed the carbs once and checked all jets and passages for obstructions and blew out with compressed air.
Can I remove the carb cover and see which carb is not delivering by operating the throttle lever? Any advice would be a big help.
Thanks

 

[Ray Neudecker]

Re: Checking Carbs

You have a somewhat complicated carb motor in that it uses a primer system that drains off the top carb as well as the other two fuel pumps.
Removing the air box cover and spraying a little carb cleaner into each barrel may help you with the trouble shooting. How does the motor run other than idling?

 

[Finley]

Re: Checking Carbs

One or more dead Cyl.
Sunday I put in the water so I could run without the muffs. She will not hit on all cyl. I really did not try to increase RPM too much for fear of hurting something.
On the muffs she really puts out oil from the exhaust which, to me, seems like a cyl is not getting fuel so not burning the oil.
BTW, the oil system, pump rod, levels seem OK. I know a broken pump rod connector goes to max oil.
I was thinking that by looking in the carb throats I could see which was not working. Maybe I'm missing something else.
Thanks for your help.

 

[yamamarinetech40]

Re: Checking Carbs

Finley,
How did you measure the spark? LIke Ray said, the best way to see if fuel starved is to spray a little carb cleaner into suspected cyl.(or each) and see if that cyl. kicks in...I mean it will react much more than others to the spray.

 

[yamamarinetech40]

Re: Checking Carbs

Also, you don't even mention the plugs...did you pull them? If a plug is fouled enough no spark is good enough to make it fire...and the cylinder is therefore dead....what did they look like if you did...should show which cylinder isn't firing....clean and put back in, run and then reinspect

 

[Finley]

Re: Checking Carbs

Here's my rundown.
Had to remove the CDI to tap one of the 6MM bolt holes that stripped when replacing the pressure relief valve. All this started after that.
1> I checked compression. (4 cyl at 120 & 2 at 115)
2> Bought a spark checker that had a dial setting to open or close the gap. I set it to the wider setting ( not sure of the width but it was for the higher output). I had spark on all 6 cyl but it was not jumping all the way across the gap. I could see spark on the the coil side of the tester contact. I thought this was OK (maybe not). Anyway, the plugs were not fouled and 2 years old with maybe 25 hours. Replaced anyway.
3> Had to replace 1 fuel pump gasket. Was leaking. Blub pumps up tight and squeezing has no effect on idle.
4> Has new Fuel/water seperator, in line filter and inside cowling filter.
5> All fuel bowls had fuel. Pulled carbs, soaked and high pressure air to finish. It appeared that all passages were clear. No sediment in bowls on removal.
6> I have triple checked all wire connections, looked for bent pins and good ground connections.
I thought that maybe my next step should be spraying before I revisit spark. First time that I've used this tester.
BTW. She fires right up but is not running on all cyl.
Hope this info helps with a suggestion. My fingers are tired now.
Thanks

 

[Ray Neudecker]

Re: Checking Carbs

Replace the fuel pumps themself. Best not to rebuild. Be sure the CDI is properly grouded even to running another wire from a good ground to it. If this doesn't cure it. The likely other source of the problem would be the fuel pump used to prime the motor. One way to test it after you have done the other two items is to plug the hose between the pump and top carb bowl. This will stop any fuel being drained off the top carb.
We do away with most of that system of pumps on the hot rod boats around here. Take a Blue Holley with the regulator set about 5 1/2lbs. Do away with the three mechanical pumps after blocking the holes. Hook up the primer through a nitrous solenoid. Have to swap out the bottom bowl on the carb and you have a very reliabile system that will deliver several times the fuel the engine willever need. Seems like it cost little more than replacing the three pumps.

 

[Finley]

Re: Checking Carbs

Ray. I only have 2 pumps on my motor. '93 225TLRR.
I'm really at a loss on what you're advising. Both pumps are 1 year old. I over tightened thus pinching/cutting the outer diaphram so I replaced outer diaphrams on both pumps. Not leaking now and seem to be OK.

 

[Ray Neudecker]

Re: Checking Carbs

Am at a loss here since your description doesn't match my memory or the parts manual. They both show the third pump used as a primer. I have a 93 and 94 model of them in the shop now. they both have the third pump on them. It is mounted at the top of the intake above the two other pumps.
Do your carbs have chokes?

 

[Finley]

Re: Checking Carbs

Probably my lack of knowledge. Mine is carb with the prime start. Is the third pump have the little red lever? With the small tubes coming out? If so, would this affect the idle? She fires right up, even cold but extremely cold natured.

 

[rodbolt]

Re: Checking Carbs

that 3rd pump with the red lever and the 2 solinoids is the prime start pump.
based on signals from the ECU it can and will alter the air fuel mixture in the intake tract.
it also has a set of diaphrams that can rupture and create idle and cold start issues.
the system worked very well if maintained and always remember with prime start DO NOT advance the throttle for cold start or starting will become difficult at best to imposible at worst.

 

[Ray Neudecker]

Re: Checking Carbs

Yes that is the third pump.

 

[Finley]

Re: Checking Carbs

Opps. wrong key.
Anyway, I believe one of the grounds was corroded. I cleaned all the grounds checked the prime start pump.
It did not help spraying gas into the carbs. Put her in the lake and adjusted the idle. She opened up quickly with no hesitation. She runs about 5100 rpm at WOT. Thanks for all the help. It is very comfortable knowing you guys are here and willing to share your knowledge.