Carb Jet Size

[Brew2]

1986 Evinrude 140 - Been having an ongoing stalling problem while accelerating. I know that it is fuel related as the problem can be overcome by bumping the primer a few times while accelerating. Once you get the RPMs high enough for the boat to plane, there are no problems.<br /><br />I've cleaned the carbs (several times), installed new carb kits, and replaced the fuel pump and all the fuel lines.<br /><br />I'm thinking my next point of attack is the mid-range jets on the carbs. I know that they are metering air, so I need to go smaller to increase the fuel flow. My question is....what would be a reasonable size reduction to determine if this is my problem?<br /><br />I know those jets run about $10-$15 each here in Canada, and I've got four carbs on my motor, so experimenting with several different sizes could get expensive. Any thoughts on what size I should start with?<br /><br />Unfortunately, I've put the boat away for the winter and its not easily accessable at this point. I do know that the jets currently being used are the sizes noted in the manual, but can't remember what they are at the moment.<br /><br />As always, many thanks to those in the know that volunteer their time and knowledge.<br /><br />Brew

 

[Brew2]

Re: Carb Jet Size

Oh yeah...almost forgot... have also done sync & link and confirmed that the timing is per the manual.<br /><br />Brew

 

[Brew2]

Re: Carb Jet Size

Dhadley,<br /><br />Thermostats in....plugs are Champion QL77JC4....fuel is fresh 86 Octane....air box is always on....inner baffle of cover? Not sure what that is...I've never noticed anything inside the air box cover, but I've never really looked that carefully. Could you describe it a little more?<br /><br />Thanks.<br /><br />Brew

 

[Dhadley]

Re: Carb Jet Size

Several things --<br /><br />Are the thermostats in or out?<br /><br />What spark plugs?<br /><br />Is the fuel fresh?<br /><br />Are you running with the airbox cover on?<br /><br />Has the inner baffle of the cover been removed?

 

[Dhadley]

Re: Carb Jet Size

Good deal. <br /><br />OK, now just bear with me a second here. Are you sure the air jets are in the correct hole? As far as idle jets in the lower hole and mid range jets above them? Them getting switched is real easy and happens more that you think. Kinda sure youre OK because you seem to have a good handle on the rest. Just one of those things ya gotta ask.

 

[Brew2]

Re: Carb Jet Size

Absolutely you gotta ask!! <br /><br />Last time I cleaned the carbs I made absolutely sure I had the jets put back in the correct hole as I was thinking that it might have been my problem. Checked each carb one by one with the manual in my hand for reference.<br /><br />Cheers,<br /><br />Brew

 

[Dhadley]

Re: Carb Jet Size

OK. Good. Does it idle OK? Or does it spit back and die?

 

[Brew2]

Re: Carb Jet Size

Typically it idles OK....although the last couple times it was out this year, I was occationally getting a small surge in RPMs at idle followed by a stall. Drove the wife nuts while trying to manouvre out of a tight docking space!!<br /><br />Thanks.

 

[seahorse5]

Re: Carb Jet Size

Next season, install the recommended QL78YC extended nose sparkplugs, gapped at 0.030". Make sure the motor is idling with a cylinder head temp above 125 degrees, decarbon the engine, and make sure it is propped to turn up close to 6000 rpm before playing with the jets. When you cleaned the carbs, did you check for cracks between the air bleed holes in the high speed nozzles and did you force carb cleaner thru each of the brass idle and midrange tubes to make sure they were clear and not plugged or restricted?

 

[Dhadley]

Re: Carb Jet Size

OK. Look at the small cover on the side of each carb body. There is a gasket behind each plate. If you have the origanil carbs I believe that plate has 2 screws. If those plates are warped they will suck air and act as you describe. Next time you run it squirt some premix or Engine Tune around those plates. If the motor straightens up momentarily then that plate is leaking. Sometimes we put a large washer under the screw to try to pull the plate flat.

 

[Brew2]

Re: Carb Jet Size

Thanks for the info guys.<br /><br />Seahorse.....I thought the QL77's were the recommended sparkplugs...I'll have to check out the QL78s. Engine was decarbed mid summer and does turn 6000 RPM at WOT. Used an aerosol carb cleaner and did force it through every orifice I could find on the carbs including the idle and midrange tubes. Checked for cracks in the carb body, but none were evident. I've never checked the cylinder head temp, but will check that out in the spring.<br /><br />Dhadley....never thought of that....I'll check out those plates in the spring as well.<br /><br />If I still have the problem and do end up playing with the mid-range jets, what would be a reasonable change in size to have some impact. I assume one size would have little to no impact...would say 5 sizes be reasonable..too much...too little?<br /><br />Thanks.

 

[Dhadley]

Re: Carb Jet Size

5 is a lot. I usually go 3 at the most and then back up one if needed. The bottom line is I think it may be OK with stock jetting if we find whats not right and correct it.<br /><br />Also look at the emulsion tubes. Thats the little tube in the center of the carb throat. Make sure it isnt erodded away some.

 

[Brew2]

Re: Carb Jet Size

Dhadley...I did notice a minor bit of erosion on a couple of the emulsion tubes. I tried getting the only dealer we have around here to get me a few new tubes from Bomb, but he advised I'd have to buy all new carb bodies. Any thoughts on how I might go about getting just the tubes?<br /><br />Thanks for all your help and suggestions.<br /><br />Brew

 

[Dhadley]

Re: Carb Jet Size

Ah, if the tubes are erooded they need to be replaced. Now the hard part -- always one of those -- thats not a part sold seperately. And there are at least 4 different ones. If your dealer isnt really really tight with someone at BRP I doubt youll get them. <br /><br />Alternatives? Used carbs is always a possibility. Dont buy just the carb bodies. Get the assembly with the throttle body. There's a ton of different ones and the calibration is matched between the carb body and throttle body. Make absolutely sure the jetting has not been changed. Keep the stock jetting. Find out exactly which motor they were on originally. Carb assemblies from a V6 will be fine. Youll just have two single barrels left over. Spare parts etc.<br /><br />Pro Marine has new assemblies for a V6 at a good price. Call and talk to Jim at 800-621-7761. They're for the 93 and newer V6's and were run with a "thumbscrew airbox" but I'm sure your airbox will work. Dont run without an airbox cover.