96' Merc 454 hard starting
08-26-2009 | 07:19 PM
#21
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Joined: Nov 2001
Posts: 3,393
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From: IBX
Do you have the choke wire tied open? If not it may be cooling and going closed when it should be pulled off by vacuum. Next time it won't start hot take of the breather and look at the choke plate to make sure it is wide open. If it is not you found the problem.
08-26-2009 | 09:59 PM
#22
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Ditto- just disconnecting the wire is not enough, as the choke will tend to close on you and the engine will run poorly or not at all. Either connect the wire, or disconnect AND fasten the linkage back to full off. I did this once and I think the symptoms are that it runs ok at idle and up to about 1500-2000 rpm, and at high rpm it then stumbles / stalls as the choke plate closes up (this is from memory back to 2000 / 2001).
08-29-2009 | 10:35 AM
#23
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From: Bird Nest
My experience is with the Edelbrock marine 750, and it was a pain to get the choke correct. Looking at the parts diagrams (this is from memory back a few years) it appears that the Webers and Edelbrock are mechanically similar. IIRC the carb line was sold to Weber way back when and thats why Webers started showing up in the carbed Merc engines.
In fact I really dislike the Edelbrock carb as it has been a real challenge to tune. Actually swapping jets and needles is easy, even on the water, but getting it performing correctly has been nearly impossible. I decided to just rebuild my original Quadrajet 795 and put that back on, and the engine is night and day differenct- better power and better fuel economy. Following the formulas indicates I need 730 cfm so I felt the Edelbrock would be sufficient. Obviously the Rocheter is far more complicated and harder to tune, but it seems to work better over the entire rpm range. That said, I prefer EFI overall.
In fact I really dislike the Edelbrock carb as it has been a real challenge to tune. Actually swapping jets and needles is easy, even on the water, but getting it performing correctly has been nearly impossible. I decided to just rebuild my original Quadrajet 795 and put that back on, and the engine is night and day differenct- better power and better fuel economy. Following the formulas indicates I need 730 cfm so I felt the Edelbrock would be sufficient. Obviously the Rocheter is far more complicated and harder to tune, but it seems to work better over the entire rpm range. That said, I prefer EFI overall.
I am a Holley guy but if I want to sell something and want it to start fast and idle quick a Edelbrock hands down will be stuck on the engine. But then again none of my Holley's have a choke.
