Testing carbs?

[Steveng]

After receiving some sound advise ( actually made sense to me), Is there a way to bench test carbs, or a way to test if a cylinder is receiving fuel???

Carbs have been rebuilt and are on a 91 Johnson 70 hp.

Thanks, Steve

 

[Daviet]

Re: Testing carbs?

The only bench test for the carb that I know of is for the needle and seat, hold the carb upright and you should be able to blow through the needle and seat. Flip the carb upside down and you should not be able to blow through the fuel inlet, needle should shut off fuel flow.
I guess you could remove the spark plugs and hold the choke on and spin the engine over and see if you get a mist of fuel out of the plug hole, never had the need to try it.

 

[patrick4266]

Re: Testing carbs?

I have that motor and manual for it. I rebuilt my carbs a while back if you need to know something ask me.

 

[Steveng]

Re: Testing carbs?

When I rebuilt the carbs, I did the blow test and all was good. The number two cylinder was in bad shape when I pulled the head off. Number 1 and 3 were ok. Any ideas?

 

[tashasdaddy]

Re: Testing carbs?

WHAT is in bad shape, tells us nothing.

the way you make sure a cylinder is "running", is to pull the plug wire, off when the motor is running. when the wire is removed, the RPMs should drop, and resume normal operation, when replaced.

if this does not happen, you have 3 possibilities. no fuel/oil getting to cylinder, bad spark ( could be plug, plug wire, coil), last is low compression.

 

[Steveng]

Re: Testing carbs?

The pistom was bad shape with melted bits stuck to it. The side was melting away. The cylinder had no compression.

 

[Daviet]

Re: Testing carbs?

Was there damage to the cylinder bore itself, or to just the piston?

 

[mrcj001]

Re: Testing carbs?

Sounds like it snapped a ring........

 

[Steveng]

Re: Testing carbs?

Yes there was damage to the cylinder, but I think it can be bored and saved. I'll know more on Monday after the machine shop looks at it. I believe the most it can be bored is 40 thousandth over, although I would not like to go over 20 if possible. If a ring snapped, what would have caused that to happen? Would I be back to the carb plugged issue, and could that have happened before I rebuilt the carbs. I will check the piston to see if part of the ring is missing and get back to everyone. Thanks, Steve

 

[Steveng]

Re: Testing carbs?

Gentlemen, a picture is worth a thousand words. Attached are some pics of the damage to the piston and cylinder. Also is a pic of the crankshaft rod journal that shows signs of heat blueing. All feed back is welcome. My plan is to have the cylinders bored and install new pistons,rings,bearings, etc. I will replace the crankshaft if needed so please chime in on the crank too.

 

[ezeke]

Re: Testing carbs?

That's fairly typical of the damage caused by air getting into the cooling system from a misplaced tell-tale outlet, which is the subject of many threads here at iboats. http://forums.iboats.com/showpost.php?p=2914937&postcount=11

That could also be caused by lugging from being over-propped or from failure to perform the recommended annual de-carbon treatment.

 

[Steveng]

Re: Testing carbs?

The water pump did require replacement when I purchased the boat. Damage was probably already started and by the time I realized it, replaced the pump, the damage was done. What would be an opinion on the crankshaft.
Can it be polished within tolerances or should it be replaced?

 

[keefallan]

Re: Testing carbs?

Unfortunately, I don't think anyone here is going to say "go ahead and use it"
You need to decide for yourself based on feel(fingers) and your gut. My response is that you have to mic it and let the #'s tell you what you need to do. I believe they'll tell you all you need to know.

 

[Steveng]

Re: Testing carbs?

Thanks to all for the input on this issue. The information especially the service bulliten were of great help. Again thanks to all, Steve