350 bog on acceloration

[dodgefate]

hi there all you great people I was woundering if i could get a little help on a problem that my brother in-law is having with his boat. He had a new engin (chevy 350) put in 3 years ago and put maby 20 hours on it. I seem to be his resident mechanic now, and when we went out the other day it was bogging on accelration. If you do a hole shot it gets up and goes and then starts to die out. If you back off the gass a little bit it will pick up. I was playing with the carb (Quadrajet) while it was bogging and if i sligley closed the secondary flaps up top it would pick up, run good for a few seconds then die back down. I think its a fuel starvation problem but i really dont know. When i worked on cars i just used to scrap the q jets for a holly or edelbrach any sujestions would begreatly appricated.

 

[jtybt]

Re: 350 bog on acceloration

Do you let go of the secondaries and it starts to bog again?
If so, it's the tension spring on the starboard side of the upper shaft. There's a little allen bolt the holds/adjusts the spring tension.

If it bogs and you keep the secondaries partially closed, it's likely the floats. Either partially stuck valve or float height too low of float has absorbed or filled with gas.

But, before you take the carb apart, check the filters.(one in carb, too)

 

[dodgefate]

Re: 350 bog on acceloration

well i dont tuch the butterflyfs for the secondarys but more like the ckoke plates for them, the engin hangs about 3400 rps..... should the lower butterflys be wide open at that rpm?

 

[Bondo]

Re: 350 bog on acceloration

Ayuh,... My guess is,.. That carb needs to be Rebuilt, or Replaced...

 

[John_S]

Re: 350 bog on acceloration

well i dont tuch the butterflyfs for the secondarys but more like the ckoke plates for them, the engin hangs about 3400 rps..... should the lower butterflys be wide open at that rpm?

The lower butterflies are controlled purely by the mechanical linkage. With the engine off you can move the throttle lever to the point the secondaries start to open, and mark the spot. To view them, gently press on the airdoor (what you are calling a choke plate) to view the butterflies.

If you have been pushing the throttle past that spot, when you get the bog, there is a good chance jtybt is correct and you need to adjust the spring tension. It is why this carb has gotten one of its many nicknames, quadra-bog.

Three years and only 20 hours tells me a lot of gas just sat in this carb. The carb could need a good cleaning and adjusting. It might be the right time to bow out as the resident mechanic, and do what Bondo suggests, or take on a off-season project.

 

[dodgefate]

Re: 350 bog on acceloration

thanks so much for the advice! I'm proplably going to look at it on monday. Ill start with the fuel filters and see if that does anything. Adjusting the spring pressure where is the adjustment screw located?

 

[Apollo75]

Re: 350 bog on acceloration

Q-jet --- If there is a vacuum diaphragm on the top left of the carb --- when you are facing the carb --- that is choke pull off and it controls by vacuum signal when the secondary air valve opens (top) --- make sure it is working properly.


Good Luck

OFM

 

[John_S]

Re: 350 bog on acceloration

Adjusting the spring pressure where is the adjustment screw located?

If you haven't already, go to the "Adults Only" sticky thread and download the manual for your boat. If it is not a Mercruiser, download #17 or earlier one for SB V8. It will have a section on the Q-jet including showing adjustment for the wind-up spring. It is not an easy access adjustment to do on the boat.

 

[n2ostroker]

Re: 350 bog on acceloration

I'm going to guess its the filter. Either in the carb or the water separator. Sounds like it runs fine till it starves itself for gas. Sometimes sediment will settle then get sucked up as fuel starts to move, or the filter element will collapse and hurt flow. Start with the filters then move to cleaning the carb. It's probably nothing that bad.