back fire through carbs

[thehookerman]

I just purchased this boat and when i try to start it it runs really rough and cant get it to idle wants to die so when i give it more gas it back fires through the carbs and smoke comes out? I noticed on the intake manifold the gasket was kinda of broke off so there is some gaps could this be some of my problem's?also checked plugs and some of them had oil on them is that a bad thing?also could this be bad gas causing this?455 olds 660 center squirters tunnel ram,11:1 comp,forged piston .any advice would be great.thanks

[78Eliminator]

First check spark plug wire order. Then do a leak down test. Let us know the results and we'll go from there. Should be the first thing you do when you get a new "to you" boat. Backfiring is generally caused by either a timing issue or a vacuum leak.

[502 JET]

If you have a vaccume leak fix that first then check your fireing order and ignition timeing.If your tune up parts are old then replace them.Depending on how long the boat sat you may need to rebuild the carbs or remove the bowls and clean out.

[Moneypitt]

I just purchased this boat and when i try to start it it runs really rough and cant get it to idle wants to die so when i give it more gas it back fires through the carbs and smoke comes out? I noticed on the intake manifold the gasket was kinda of broke off so there is some gaps could this be some of my problem's?also checked plugs and some of them had oil on them is that a bad thing?also could this be bad gas causing this?455 olds 660 center squirters tunnel ram,11:1 comp,forged piston .any advice would be great.thanks
How long did it sit? and did you hear it run when you bought it? And how old is the gas?......It sounds like a combination of everything, bad gas, dirty carbs, vacuum leaks, etc. etc.......A little more info might help.........MP
PS.......The backfiring is caused by a lean condition. Probably lazy accelerator pumps, meaning the squirt is late, or weak and can't supply enough fuel to match the extra air when the carbs are opened. Same effect from a vacuum leak, lean..........I would suggest you either rebuild the carbs or have someone do it for you, and do a little spray test along the intake areas you think might be leaking vacuum. DO NOT reinstall rebuilt carbs unless you are sure there is not an intake manifold leak..........MP

[thehookerman]

yes the motor was running when bought but it was at a higher elevation 5000 ft the boat now is in san diego don't know if that's a problem to .I would guess it sat for winter? but I'm going to start with intake gasket do I have to know what year the motor is to get correct gaskets and if so how do you go about finding out year?

[Lavey Huffer]

try spraying starting fluid in the suspected vacuum leak areas and you will hear the rpm's change then you know you have a leak.

[Moneypitt]

DO NOT spray starting fluid around an engine that is backfiring!!!!! Unless you got some real good boat and LIFE insurance.....Use something less volitile, like gumout or even gunk. All you want to see is IF the liquid gets sucked in, then stop, you've seen enough. You could even use Marvel Mystery oil. If the motor starts smoking, guess what, it's sucking the oil in..DO NOT use starting fluid........(bomb ina can)...........MP

[thehookerman]

I hear you loud and clear mp. I'm going to replace the gaskets all together tomorrow and see where that gets me. far as cleaning the carbs what should I do just spray em down with carb cleaner?

[Moneypitt]

What your carbs need cleaning wise, is internal, not external. Now, if the motor ran prior to purchase, how long ago was that? If it were tuned for 5000 ft elevation, it may need to be jetted for sea level, but that won't cause what you discribe. If it ran decent before, chances are you don't have a vacuum leak, but here again, how long since it ran?......With the motor OFF, remove aircleaners, put your face right on top of the carb,(either one), and ever so slightly move the throttle shaft, 1/16th inch, did the squirter squirt? This test is at rest. Not after pumping it a few times. What you are checking is the accelerator pump check ball/pin directly under the nozzle assembly. If you have to pump it again to make it squirt, then that is a lot of your problems....Again, the slightest movement of the throttle shaft MUST be rewarded with fuel from the pump/squirter. Anything less is going to lean the motor out, make it stumble, and bang back thru the carbs, which wastes the power valve diaphrams and makes it rich all the time.......If the motor ran last month?? What, if anything, have YOU done/changed??? Lets address that first........MP

[JMC]

Tuned at 5,000 feet above. You may have a lean condition now that it's close to sea level.

[78Eliminator]

hookerman, got a digital camera? you know what they say, a picture is worth a thousand words.

[thehookerman]

yes the squirters did squirt when moved a 1/16 and Ive really have done nothing to the boat besides clean every thing.and its been about a month or so since it ran last.

[Beer-30]

Cracked cap? Carbon inside cap?
If he's popping back through, he'll be needing power valves.

[Moneypitt]

yes the squirters did squirt when moved a 1/16 and Ive really have done nothing to the boat besides clean every thing.and its been about a month or so since it ran last.
Did you clean the motor? Look inside the dist cap for moisture, around the coil conections/wire.. You also said you looked at the plugs, ANY chance the wires are crossed? There are only 3 things needed to run, fuel, which you have,(at least in the accelerator pump circuit, pull a "sight" plug and see if the bowl is full) Air, which there has to be, and spark at the right time. With those 3, it ought to run. You might try choking it a little with a rag across PART of the carb(s). Do the carbs have secondary idle circuits, and "all" at once linkage? It is true that you may not get the best performance at sea level if it was tuned @ 5000ft., but it should still start and run. Banging and popping usually points to ignition.......Check inside the cap, and verify the firing order and plug wires........18436572......COUNTERCLOCKWISE, (it's an Olds)...............MP

[thehookerman]

ok just removed gas and put new gas in with octane booster .boat started up with no back fire but still wouldnt sit at idle?throttle adjustment?or carb adjustment?

[Moneypitt]

It may be adjusted for the 5K elevation. Try restricting the air flow. If that helps, then fatten up the idle mixture. Remember, it's cold, warm it up and see if it changes. The main jets do not play a role in the idle circuit unless the butterflies are cracked open a little at idle......I can't see waek gas being the major problem, but if new gas helped then I guess it was playing a part..............MP

[blowngas]

motors that have a blown head gasket will backfire thru carb---if gasket is blown and ran too long, you can torch a slot between cylinders taking out the block and sometimes head----don't just think ignition, or carbs!!!-----run compression check or leakdown and rule out head gasket

[Zeug]

Hey, Whoa,
Hookerman email me or PM me. I am offended you didnt call or ask me, the previous owner for help. :)
The boat ran great last season at 5000'. You most likely need to fatten up the jetting. The boat wont idle until it is up to temp! Just like every boat I know. Make sure you warm it up in the water.
Also, if you backfired through the carbs, you may need to look at any damage there. Possibly messed up something.
Kent

[HOSS]

Like broken valve springs. :cool:

[Moneypitt]

Nah Hoss, just sea level lean and cold......Alot more air in the air down here by the beach.............Ray