Nissan 3.5B idle too high

brewster1

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Jun 27, 2021
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Just put a rebuilt carb I bought online onto my 3.5b but the idle is about 2500 rpm and looks like the end of throttle travel. how do you adjust idle speed?
 

Sea Rider

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Sep 20, 2008
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Welcome to IBoats,

Is that a 2 stroke M3.5 B2 motor ? Why did you changed the previous carb for ? Those carbs have an internal Jet Needle attached to a circular Throttle Valve which it's adjustable by means of a Jet Clip, at which upper or lower groove does the clip rests to ?

Happy Boating
 

Sea Rider

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Sep 20, 2008
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it was stalling out after 3min
so rebuilt carb
how to slow the idle?
So the motor doesn' stall when at high revs, right ? That carb has a rubber o'ring located right in between the manifold's neck and the carb's rear body, if missing too much air will be introduced and surely the motor will rev high, check if having it, if not, will need to order part no : 309-031162 - (0'ring 2.4)

Happy Boating
 

brewster1

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Jun 27, 2021
Messages
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So the motor doesn' stall when at high revs, right ? That carb has a rubber o'ring located right in between the manifold's neck and the carb's rear body, if missing too much air will be introduced and surely the motor will rev high, check if having it, if not, will need to order part no : 309-031162 - (0'ring 2.4)

Happy Boating
unfortunately, the O ring is in place so that is not the problem with the high revs. I guess I dont really understand how a 2 stoke carb works. is there a low speed jet and a high speed jet? can you adjust the low speed. the screw on the side with the spring over it does what?
 

brewster1

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Jun 27, 2021
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unfortunately, the O ring is in place so that is not the problem with the high revs. I guess I dont really understand how a 2 stoke carb works. is there a low speed jet and a high speed jet? can you adjust the low speed. the screw on the side with the spring over it does what?
actually full story is that last season it would easily start and run well at idle and low speed but when given higher rpm would stop and not re start. so i bought a new rebuilt carb which is what is on it now with the high idle.
I also took out th little tiny fuel filter in the internal fuel tank which although clear seemed like a possible fuel starvation issue.
 

MattFL

Chief Petty Officer
Joined
Oct 20, 2010
Messages
512
A "new rebuilt" carb is not new so that's a possible red flag. Also removing a fuel filter is never a good idea, the manufacturer would have put one in with sufficient fuel flow (if it's clean) and removing it is just asking for problems caused by debris getting into things like the carburetor. My first advice would be properly clean the old carburetor and try that one since you're sure it's the right one for the motor. My second suggestion would be, if it's got a fuel screw, then on the old carburetor count how many turns it takes to turn it all the way in (not very tight!). On the new carburetor, turn the screw in all the way, then turn it out the same number of turns that the original carburetor had. This would be the best starting point for tuning it. If the motor is revving too high at idle then it's getting too much air somehow. Either the throttle is open too far, the idle circuit is open too far IF it's a carburetor with a separate idle air circuit, it's the wrong carburetor for the motor or there's an air leak somewhere.
 

Sea Rider

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unfortunately, the O ring is in place so that is not the problem with the high revs. I guess I dont really understand how a 2 stoke carb works. is there a low speed jet and a high speed jet? can you adjust the low speed. the screw on the side with the spring over it does what?

Salute the wild guessing about this particular 2 stroke motor carb. Have never ever had issues with those small portable motors and regularly servicing 20 of them. To begin with, those have a mesh fuel cok located under the tank, will be mission impssible to produce high revs as described, usually clogs and shuts motor down due to fuel starvation. I'm lost, are were talking about the same carb which was entirely rebuilt with a new carb kit or we're talking about two different carbs ?

These carbs have only one speed jet with 4 adjustable grooves heights that controls the mixture for the motor to run lean or rich housed inside a circular throtle valve, the side screw with an attached spring controlls the idle rpm, turn it CW or CCW and check if lessens the high rpm.

Happy Boating

 
Last edited:

brewster1

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Jun 27, 2021
Messages
8
thanks for the info sea rider. the problem was that the new rebuilt carb i installed had the adjustable groove height too low and that made it idle too high. I moved the little washer and now all is well. i did not understand how that worked. but now i do
 

Sea Rider

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Carb Tech Specs :

If being a 2.5A / 3.5A / 3.5B motor the Main Jet calls for # 92.
If being a 2.5A2 / 3.5A2 / 3.5B2 motor the Main Jet calls for # 86.

All 6 models comes factory delivered with the Jet Needle Clip Goove set second from bottom...

Happy Boating
 

brewster1

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Joined
Jun 27, 2021
Messages
8
Carb Tech Specs :

If being a 2.5A / 3.5A / 3.5B motor the Main Jet calls for # 92.
If being a 2.5A2 / 3.5A2 / 3.5B2 motor the Main Jet calls for # 86.

All 6 models comes factory delivered with the Jet Needle Clip Goove set second from bottom...

Happy Boating
thanks. what would you recommend a source to obtain main jets.?
 

brewster1

Cadet
Joined
Jun 27, 2021
Messages
8
i cant find the reference to a #92 needle valve.
the nissan number i found in the schematic is 3F0031533
 

pvanv

Admiral
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Apr 20, 2008
Messages
6,274
Any dealer.
309031471MNEEDLE VALVE$7.68
*ALSO NEED 309031481M*
3D7031480MSEAT, NEEDLE VALVE Part 309031481M was superceded to 3D7031480M$8.98
 
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