Extreme surge after extended idle '78 Catalina Express Cruiser

sgswrench · 06-04-2008, 02:55 PM

I am the proud owner of a '78 Catlina express cruiser. I inherited the boat from my deceased father-in law and have been restoring/cruising for the past 6 years. As an auto shop owner of 30+ years, I have a little bit of mechanical comprehension. The engine was replaced last year and upgraded to the 350, we also added electronic ignition. We can now cruise at 3200, 25 mph, at 8.2 GPH! The problem we have is after cruising a while (warmed up), and then idling for 5 minutes or so (like in a no-wake zone) and then re-applying throttle, I get a very extreme surging from a near stall up to 3000 rpm, the cycle from near stall to rev-up is about 1.5-2 seconds, and it will surge for about a minute, decrease in intensity, and then go on down the bay like normal. This condition was prevalent with the old engine as well (we've had this symptom for the past 3 seasons. I can't be sure, but I believe after 1 of the exhaust manifolds was replaced the symptom surfaced. I suspect maybe the fuel filter (bolted to the front of the starboard exhaust manifold) or the fuel line may be heating up and vapor locking. I'm hoping one of you kind souls has seen this before and can help get my pointed head facing the right direction !!

Ken Bracewell · 06-04-2008, 03:16 PM

Are you using the same throttle controls as the old engine?

sgswrench · 06-04-2008, 03:18 PM

Quote:

Originally Posted by Ken Bracewell

Are you using the same throttle controls as the old engine?

yes, and the throttle is being applied to the carb exactly as it is when the engine is not surging (not a throttle linkage issue)

sgswrench · 06-04-2008, 03:20 PM

Quote:

Originally Posted by Ken Bracewell

Are you using the same throttle controls as the old engine?

she will even give me a lean backfire if I apply too much throttle during these symptoms

sgswrench · 06-04-2008, 03:21 PM

Quote:

Originally Posted by Ken Bracewell

Are you using the same throttle controls as the old engine?

we did have these symptoms with the old engine as well

NYCAP123 · 06-04-2008, 04:01 PM

I'm no mechanic, but I've seen similar symptoms several times. That 3200 cruise is puzzling as it should max at about 4600, cruise at about 3800. Generally when swaping engines you try to save where you can. Any chance the carb or fuel pump was brought over? Whether or not my guess would be a bad or clogged jet/ choke or pump in that order.

sgswrench · 06-04-2008, 04:24 PM

Quote:

Originally Posted by NYCAP123

I'm no mechanic, but I've seen similar symptoms several times. That 3200 cruise is puzzling as it should max at about 4600, cruise at about 3800. Generally when swaping engines you try to save where you can. Any chance the carb or fuel pump was brought over? Whether or not my guess would be a bad or clogged jet/ choke or pump in that order.

I'm having trouble with a consistent intermittent clog, that goes away, and will come back only after warm and extended idle, then it clears itself out? not some kind of vapor lock or carb icing??

sgswrench · 06-04-2008, 04:55 PM

By the by, the fuel pump is new, carb overhauled (remember, same symptoms, 3 seasons) and she will crest 4600, and she can cruise at 3800, just not as economically.

NYCAP123 · 06-04-2008, 05:06 PM

The problem only surfaces when the engine is warm (metals expanded, holes contracted). New pump is good, so I'd look at the recon. carb. It only takes a spot of dust in that jet or a wrong jet. Warm it up, spritz with carbmaster and see if there is any change in range of surge (won't fix, just tell if on the right track).

sgswrench · 06-05-2008, 07:30 AM

Thanks for the reply.... yes, if I get carb cleaner or brakecleen (alcohol) to the flame arrester, she'll light right up (as long as I enrich) but I really do not think its a clog or restriction in the carb. How does it disappear, gradually over a 1 minute attemp to re-accerate? New news, however, I seem to be missing 2 aluminum spacers between the exhaust log and the fuel filter housing. (I have the old canister filter, new element this season, of course) I think log heat may be boiling my fuel and vapor-locking the filter. I'll let you know, off to make some spacers.........

sgswrench · 06-09-2008, 11:05 AM

I Have to tell you Cap< I did not fix my surge (which was even worse this weekend in the 95 degree heat) but I did cruise at 3600, dropped to 6gph and picked up 5mph, I could kiss you. (good thing you're not here)

NYCAP123 · 06-09-2008, 11:28 AM

I'm still betting on that carb. A bad jet is nearly impossible to see and easily missed on a rebuild. Have a good summer.

Seafarer · 06-09-2008, 01:09 PM

Have you checked to ensure the fuel tanks are venting properly?

Assuming, of course, that's it's an engine/fuel delivery problem and not cavitation around the props until they bite into the water at a certain speed...

NYCAP123 · 06-09-2008, 01:53 PM

That would be evident with a cold engine as well would show most coming out of the hole and would overrev the prop, not surge the motor. I'm remembering a boat that used to come into a transient marina I dockmastered. He went through 2 rebuilt carbs and I finally refused to allow him in. Then he splurged for a new. Problem gone.

Seafarer · 06-09-2008, 03:24 PM

Quote:

Originally Posted by NYCAP123

That would be evident with a cold engine as well would show most coming out of the hole and would overrev the prop, not surge the motor. I'm remembering a boat that used to come into a transient marina I dockmastered. He went through 2 rebuilt carbs and I finally refused to allow him in. Then he splurged for a new. Problem gone.

You're probably right, but the comment that it happened when resuming speed from a slow crawl was what put the question in my mind.

Accelerator pump, proper jetting, and plugging of the fuel line or vapor lock would probably be good things to check. Also, any garbage in the bottom of the tanks that might lift into pickups and cause lean situations.