Mercruiser 4.3 lx WOT

[achris]

Re: Mercruiser 4.3 lx WOT

If that 12" reading is steady (gauge not fluctuating) then it may be a timing problem. If the timing appears good, check that the balancer hasn't slipped and giving you a false timing indication....

Chris.......

 

[dozerII]

Re: Mercruiser 4.3 lx WOT

If that 12" reading is steady (gauge not fluctuating) then it may be a timing problem. If the timing appears good, check that the balancer hasn't slipped and giving you a false timing indication....

Chris.......

The gauge flutters a little, but for the most part is steady, The balancer looks good. Could this problem be in the Thunderbolt ign. When I adjust the timing the mark is a little erratic with the light?

 

[aerobat]

Re: Mercruiser 4.3LX WOT NOW WHAT???

Re: Mercruiser 4.3LX WOT NOW WHAT???

Thanks Chris and Bondo.

I just went out and checked the Accel pump and I get two good streams of fuel when I stroke the throttle. Could this problem be from combining the two carbs?

no. when it bogs on sudden throttle but after a second runs fine its for sure the acc pump. its not only it gives a stream at all but also it gives the right amount at the correct time. when e.g you pump shots fuel too late you will have issues even when seeing a stream at all.

there is an adjustment screw on the acc pump lever . screw it down and report if it improves - when yes, screw until no bogging anymore.

how do i know ? i had the same issue on carb rebuild and had to find out the problem after an expensive call to holley performance from europe.

( they were very knowledged and helpful and pointed me in the right direction )

 

[dozerII]

Re: Mercruiser 4.3LX WOT NOW WHAT???

Re: Mercruiser 4.3LX WOT NOW WHAT???

no. when it bogs on sudden throttle but after a second runs fine its for sure the acc pump. its not only it gives a stream at all but also it gives the right amount at the correct time. when e.g you pump shots fuel too late you will have issues even when seeing a stream at all.

there is an adjustment screw on the acc pump lever . screw it down and report if it improves - when yes, screw until no bogging anymore.

how do i know ? i had the same issue on carb rebuild and had to find out the problem after an expensive call to holley performance from europe.

( they were very knowledged and helpful and pointed me in the right direction )

Thanks for the reply Aerobat, but on the Rochester carb the only adjustment is the hole in the linkage and it is in the right one.

 

[aerobat]

Re: Mercruiser 4.3 lx WOT

i cannot say for rochester because only had hands on holleys. what you are talking is the position of the pump cam - there is no further adjustment for the acc pump ?

you may try to find a repair manual from rochester what exact procedure they have for adjusting.

further - at least holley provides different nozzles which spray in the intake - is this the same at rochester ?

good luck - i today made a testdrive after carb rebuild and also still have somme issues to sort out ;-)

 

[alldodge]

Re: Mercruiser 4.3 lx WOT

To find out if your balancer moved crank it over by hand and it doesn't matter if your TDC or 180 so long as the piston is at the top of stroke. If you have a dial indicator that is best but if not, we can do it poor boys way. Rotate crank utill No. 1 gets to the top. Use something like a wire that you can see as the piston moves up and down. When the piston stops moving up mark the balancer, then continue untill it starts moving again and mark it on the balancer. Move the crank forward and backwards until your pretty sure you have both sides; the distance between the two is TDC. Don't bother with timing chain slop because it doesn't mater.

To use poor boys timing tape, measure the distance on the balancer between TDC and 10 degrees and mark it on a piece of paper. Take the paper and a good ruler, and measure out the repeated distance for 40 degrees. Take the paper and lay aganist the balancer and transfer the marks.

 

[dozerII]

Re: Mercruiser 4.3 lx WOT

i cannot say for rochester because only had hands on holleys. what you are talking is the position of the pump cam - there is no further adjustment for the acc pump ?

you may try to find a repair manual from rochester what exact procedure they have for adjusting.

further - at least holley provides different nozzles which spray in the intake - is this the same at rochester ?

good luck - i today made a testdrive after carb rebuild and also still have somme issues to sort out ;-)

Thanks again Aerobat, there is just the one adjustment on the pump rod, good luck with yours.

To find out if your balancer moved crank it over by hand and it doesn't matter if your TDC or 180 so long as the piston is at the top of stroke. If you have a dial indicator that is best but if not, we can do it poor boys way. Rotate crank utill No. 1 gets to the top. Use something like a wire that you can see as the piston moves up and down. When the piston stops moving up mark the balancer, then continue untill it starts moving again and mark it on the balancer. Move the crank forward and backwards until your pretty sure you have both sides; the distance between the two is TDC. Don't bother with timing chain slop because it doesn't mater.

To use poor boys timing tape, measure the distance on the balancer between TDC and 10 degrees and mark it on a piece of paper. Take the paper and a good ruler, and measure out the repeated distance for 40 degrees. Take the paper and lay aganist the balancer and transfer the marks.

Thanks for the info Alldodge, I will check that out this weekend, that should also allow me to check for full advance from the Thunderbolt.

 

[dozerII]

Re: Mercruiser 4.3 lx WOT

A little more info, I pulled the plugs to check the timing marks for TDC, they are all really black and sooty, so even though I used both the old and new carb too try to compensate for National Carbs screw up I'm still too rich. I have an Edlebrock 1409 on the way, so I'm hoping that is going to fix this problem once and for all.

 

[dozerII]

Re: Mercruiser 4.3 lx WOT

Last update, fixed finally. Installed the 1409 and the performance and speed improved considerably, but I then experienced a slight pop/backfire at wot. After checking everything again and not finding a problem I called an old very knowlegable Mercruiser mechanic, explained what was happening and what I had already done. About the third thing he asked was what type of plugs I had in the motor, I said Autolight, without any hesitation he said that is your problem, put the proper AC Delco MR43T plugs in and go have fun. I got the plugs and no more pop/backfire go figure.
Thanks to everyone for there help on the problem