|
Have someone that is a marine engine mechanic look at both engines before you have two cast iron slugs that need to be rebuilt.
|
The fact it was backfiring at idle, tells me somethings jacked up. 2 degrees of timing shouldnt be the difference of backfire vs no backfire at idle. Ive had engines that idled at 8*and 36* , never had backfire at idle.
either the firing order is screwed up, valvetrain is screwed up, etc. Is the timing pointer an adjustable type ? |
I had a Holley Red pump on my boat from the previous owner and with a 454 and you could watch the pressure drop just by blipping the throttle and slowly drop down to 3psi while under way. It also was stuck at 3500rpm. I put the stock mech pump and got my revs back and gained 15mph. You may have pressure but that doesn’t mean that you have enough volume. |
What set up requires both a mech pump and electric? I’m genuinely curious. And I can’t stress enough how crappy those Holley red pumps are. It wouldn’t support my stock 454 even at an advertised 97gph |
Some additional data I forgot to mention.
The carbs (QFT 850) sat on my garage floor for 2 months while the motors were out. There was definitely some ethanol-containing 93 octane in there when the carbs were taken out of service. During yesterday's run, it almost seemed like the opening of the secondaries didn't make any difference in power. I pulled the throttles back a few clicks from WOT with no discernable drop in power. |
So you tried swaping wires for the 7&4 swap like you mentioned you were gonna try regardless that skip said they were std. No cam cards came with builds. They just rebuilds or did you purchase from him. Sounds like engines never ran right from day one. Also both electrical and fuel issues. As long as your certain fuel pressure is holding at WOT then find any 850 or 950 holley or what ever and try it out along with any GM hei. A few clicks from WOT won't necessarily make a dif as long as your blades are open fully depending on your cable and carb linkage adjustments. Id be doing three things very quickly. What power are these 540's suppose to be? Like 550 hp? I don't get any of this right from the start. Makes my head hurt. 1,500 rpm dif is like 3 cylders. This has to be driving you out of your mind. Seriously. |
Originally Posted by ancho
(Post 4658363)
Update:
Finally got everything back together and got out on the water. New plugs/wires/caps/rotors. Base timing set to 22 degrees. My cooling issues have been resolved - the addition of circulating pumps to both motors, instead of crossovers, has brought temps down to 110 on both motors. Oil temps run a little warmer on starboard motor (210 vs 180 at sustained 3500 rpm). With the old setup (crossovers) I was seeing water temps of 190-210 degrees overall and a 40-70 degree differential between cylinder heads. Max speed I saw was 56mph, and max rpm was about 3700-3800. That was WOT with a good amount of trim. So I'm short about 1500 rpm (rev limiters set to 5200) and 20mph. Timing was set to 22 degrees on starboard motor and 24 degrees on port motor, as the port motor needed the extra 2 degrees to keep from backfiring through the carb at idle. I did get another mph or 2 out of it after bumping up the timing so it sounds like that may be the solution here, but I'm worried about too much timing at the top end. After about an hour of running around at 3000-3500 rpm, the port side of the transom and underside of the swim platform was sooty. starboard side was clean. New electric fuel pressure gauges showing 6-7psi as they should, thru Holley red electric pumps and mechanical pumps on the motor. |
Originally Posted by Baja Rooster
(Post 4658425)
What set up requires both a mech pump and electric? I’m genuinely curious. And I can’t stress enough how crappy those Holley red pumps are. It wouldn’t support my stock 454 even at an advertised 97gph |
Originally Posted by Full Force
(Post 4658510)
22-24 degrees? why so low?? sure not 32-34?
|
Originally Posted by getrdunn
(Post 4658475)
So you tried swaping wires for the 7&4 swap like you mentioned you were gonna try regardless that skip said they were std. No cam cards came with builds. They just rebuilds or did you purchase from him. Sounds like engines never ran right from day one. Also both electrical and fuel issues. As long as your certain fuel pressure is holding at WOT then find any 850 or 950 holley or what ever and try it out along with any GM hei. A few clicks from WOT won't necessarily make a dif as long as your blades are open fully depending on your cable and carb linkage adjustments. Id be doing three things very quickly. What power are these 540's suppose to be? Like 550 hp? I don't get any of this right from the start. Makes my head hurt. 1,500 rpm dif is like 3 cylders. This has to be driving you out of your mind. Seriously. I totally forgot to try the 4/7 swap of the wires when I was out on Saturday, unfortunately. The motors were in the boat when I bought it earlier this year. They had 24 hours on them. |
| All times are GMT -5. The time now is 08:32 AM. |
Copyright © 2026 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.