I have a slight stumble just off idle. Sorry I can't remember exact popoff presure but was thinking above 35-40. low speed jet not sure now. low speed screw set about 5/8 open. If I open screw more than 1 1/4 the motor dies when I crack the throttle, setting it back to 5/8 it won't die but still has a stumble. But now it acts like its too rich. I was thinking if the motor dies It is too lean and if it's too rich it takes awile to rev up because of too much fuel to burn. I know 1 turn out is ideal but am I still to lean with my pilot jet. or pop off pressure not set correctly yet and if so should i go up in pressure or down? I have EWCI that is unpluged when I'm testing. I had 38 twins ported by Harry Group K. I recived carbs back with popoff set crazy low and it ran way to rich( like not able to get out of wake zone because motor ran so boggy) until I increased pressure. This is why I''m confused. It makes me think I'm still to rich with closing low speed screw but the motor dies if I richen it up. Motor should bog not die if rich right?
Blaster 701 38 carb tunning
- Thread starter catpower
- Start date
What F/A are you running with?
The low speed screw is only for adjusting your idle mixture.
Read this 3 times http://www.mikuni.com/pdf/sbn_manual.pdf
The low speed screw is only for adjusting your idle mixture.
Read this 3 times http://www.mikuni.com/pdf/sbn_manual.pdf
Yes thank you but I have read many times in past years. I've played with pilot jetting several sizes each way in past but could not tell much deference in the way motor responded. And dont even get me started on changing main jet. Waste of time observing rpm change. Anyway back to low end responce. Ive had much more low end responce changing low speed screw. Group K has a good right up also. Sorry for not finding the exact sentence written by Harry but I'm pretty sure he talkes about changing pilot jet if I can not obtain a good idle setting near one turn out. If nothing else I'm obviously compensating for an incorrect pilot jet and or pop off setting with low speed air screw. FA on a 701 b1 is all for show, not likely to be compared to other more restrictive factory FA. Tau Citi if I'm saying that correctly is what I have with water protective socks. The modded 38 carbs would indeed reduce air restriction and would demand a lower pop off pressure. But I recieved these carbs back with 20-25 PO. Low end response absolutely sucked. Just so I could ride that day I had low speed screw almost completely closed to compensate for an overly rich condition. At least that is how I describe it. Again will a motor die when I crack the throttle if my pilot is too rich, I think not. A low pop off would indeed give a rich condition vs a very high PO I'm just trying to understand if I should increase or decrease pilot and as I'm thinking maybe lower PO just a tad. Assuming a motor dies if it is too lean below 3/8 throttle. The motor starts good with out opening throttle so that leads me to think my pop off and low speed screw is set correctly. Again does a motor die if I'm lean or rich and what changes do I need to make ?
If you compensate for a rich mixture with the low speed screw you will find that the engine hesitates or die right of idle. The pop off comes a little sooner. Try to run the boat at 1/4 throttle for about a minute then open throttle. Does it hesitate/dies or loads up? I would try to increase the pop off until it hesitates and then back one step.
And make sure you have a fresh set of needle and seats.
And make sure you have a fresh set of needle and seats.
At 1/4 throttle this engine starts to take off like a rocket, so maybe more like 1/8 open?. I've done that test several times before to tune out problems. I'm having trouble identifying if I'm running rich or lean. If it dies I must be lean right but increasing pop off would lean out fuel flow at low throttle position correct. It must be a combination of pop off and low speed jet that needs to be adj. I am never sure if the motor is lean or rich. Some say if u ride below 1/4 throttle for about a minute and open up and the motor doesn't pick up rpm it is rich. If it hesitates its lean, does hesitate mean the engine dies. Because hesitate is a poor way to describe an engine that doesn't rev up. A boggy engine to me is like when water gets sucked into the motor, I guess they should describe hesitates as motor wants to die if it's lean? Correct?
I read your post again Marty and you seem to think i'm rich. I just can't get that idea of being rich out of my head with motor dieing. I keep thinking of carbs that have an accerator pump that shoots gas in the engine just off idle. Makes for great accereration. too bad these carbs don't have that.