Mercruiser carb question

I have a 1983 Mercruiser 305 GM, 128hp engine which I'm going to be putting into a 20' Sunrunner. The engine came with a Holley 4-barrel, not original. I have a rebuild Rochester 4-barrel from my previous boat. Should I leave the Holley or go back to the Rochester? By the way, following this site's advice, I redid the compression test, 145-150 on 7 cylinders, 100 on #6. Will do leakdown test next week. Suspect bad lifter or exhaust valve.

Re: Mercruiser carb question

Which carb do you feel more comfortable with?
Does the Holley have the correct linkage adapters?

Re: Mercruiser carb question

I know the Rochester from my years as a mechanic; rebuilt quite a few of them. The Holley has all the necessary adaptors; it's on the engine now. I've forgotten a lot about the Holleys; though I remember that they can be difficult to adjust properly. I've never worked on a marine Holley. Bottom line, I'm more comfortable with the Rochester.

Re: Mercruiser carb question

Bottom line, I'm more comfortable with the Rochester.

Click to expand...

Ayuh,..... Then That's the 1 you should install.......

Re: Mercruiser carb question

Re: Mercruiser carb question

What is the Holley Carb, 600 squarebore or 650 spreadbore?

If the Holley carb is marine it will have promenent J-tube vents.

If it is a Holley squarebore, you will have to check intake to make sure it is not an aftermarket squarebore only.

If the Holley is marine and engine was running welll with it, I'd wait to you get through all your other issues before swapping to Q-jet. You want to limit or reduce variables, not increase them.

If your old Q-jet did not come off a 305, you will want to make some additional adjustments, and possibly some jet/rod changes.

Re: Mercruiser carb question

Thanks for the advice. It's definitely a marine Holley; it's got the J-tubes on top. I bought the engine through the marina's mechanic. A friend of his, also a marina's mechanic had taken it out in a repower. The previous owner had first replaced his Rochester with the Holley to get more power. When that didn't work,(no surprise there) he replaced the engine with a 350. (no surprise there either), The engine looks good, the manifolds and risors look almost new inside and out, and it came complete with everything, including a remote ail filter! The price was also right too. I may have to do a valve job, but that's no big deal. The only thing missing was the coil, but I've got one from the cracked engine I'm removing from my SunRunner. I think I'll put on the Rochester. It's from the 350 that was in my old boat and only has 35 hours' use on it. I've spent part of the last month going through the 900+ pages on the site, reading everything which might relate to my boat project, downloading all pertinent information. Thank you all for your knowledge and help. I'm sure I'll have some more question, and will try to offer advice based on my knowledge and experience. Safe Boating, all. Hy

Re: Mercruiser carb question

The Q-jet from a 5.7LX or 260 ( a 350 with low-profile 4brl intake) will be fairly close to what you need. The air-door adjustment, along with the idle mixture and idle speed should be sufficient. If it came from a 350 Mag it would be on the very rich side, for your needs.

Re: Mercruiser carb question

I had bought the Q-jet when I refurbished my previous boat, a 1980 Classic 25' Sportscruiser. I had put a rebuilt 350 into it, the old points-distributor model. It ran great until the outdrive water pump housing cracked and she overheated. Put her away last season and when I went to get her ready in May I found that the keel had collapsed from core rot. I had to strip her and scrap her. Only put 35 hours on her after spending 3 years rebuilding her. But that was a labor of love and I enjoyed it, which is why I'm doing it all over again!. HY=y.