View Full Version : idle and acceleration problem
04-06-2005, 04:57 PM
Hello all. Great forums with a wealth of info. I was wondering if you might have any suggestions for the problems I have been experiencing.
I've got a 1980 prostar with the 351 engine. It has the holley 4 bbl carb.
This boat has been in the family since it left the factory and has been serviced regularly.
Last summer it was running great until near the end of the season when we started having two problems. After warming up the idle would become rough. Specifically, the engine would cycle through a series of "surges." Almost like someone was applying throttle and backing off over and over again. Each surge lasts about a second and then the engine would almost die and then surge again. If you can imagine a repetitive throttle, back off, throttle, back off, throttle, back off...I could only break the cycle by bringing the boat up to speed and then returning to idle. The second problem was with hesitation during acceleration. The engine would almost die and then suddenly pick up. In fact, sometimes it would die.
Both of these problems only occurred when the engine was up to temp. The engine never overheated. Both problems were inconsistent as sometimes we skied for hours with no problem at all. However, the problems did become more and more frequent toward the end of the season.
I planned to have the carb professionally rebuilt over winter. In fact, I did replace the secondary diaphragm myself and did an overall inspection of the carb at the end of last year but that didn't seem to help.
Now I'm considering the breaker points as the problem instead of the carb. I've decided to install the electronic ignition conversion kit before paying someone to monkey with the carb.
I was wondering if anyone else has experienced a similar problem. Hesitation before accelerating is fairly common, but I've never heard anyone describe surges during idle. Anyone?
Do you think the electronic conversion will help?
Also, do I need to remove the resistor after installing the conversion? I think I read somewhere you should.
Thanks for your time and appreciate any suggestions.
04-06-2005, 05:04 PM
Welcome to the site! My '91 came with the electronic conversion already done, but I think it's a relatively simple job anyway. Whether that is your problem or not I would still do it, you'll be glad you did in the long run. I'm still learning how to diagnose things like this, but I think it sounds like a carb problem. I just rebuilt mine myself, it was pretty easy, I bought a kit ofr $45 had everything I needed. I'll have to get back to you though on how well I did, I haven't had a chance to run it since finishing :D Anyway, I'm sure some more folks will chime in with better advice than me, but I say install the new ignition and rebuild the carb. :twocents:
04-06-2005, 05:14 PM
It does sond like a fuel problem to me as well. Maybe a dumb wuestion but did you already check your fuel filter as well as the screen in the tank for debris? I would check these things first before doing any other work. You might just have some 'junk' caught up somewhere.
Do change to electronic ignition it will make life easier. Yes you do remove the resister when installing. If you are fairly mechanically inclined the swap is only about a 30 minute job.
east tx skier
04-06-2005, 05:18 PM
I had a hesitation with accelleration issue that was fixed with a rebuild (even though I ultimately ditched the carb due to hot stall issues). In addition to the fuel filter and tank screen, check the screen where the fuel line meets the carb.
Also, this probably isn't the culprit, but cleaning your flame arrestor is always a good idea.
04-06-2005, 05:57 PM
From your description of the problem it sounds like your engine is 'loping'. This may be caused by an intake leak somewhere. I would think that it is a fuel problem and not electrical for sure. It's quite cheap and fairly easy to rebuild the carb so I would do that. I would carefully check the intake manifold gasket and the gaskets between the carb and the spacer and the spacer and the manifold as well. If it's a 1980 carb and it has not been redone yet then it is due for sure and that, plus maybe some new gaskets, will in all likelihood solve your problem.
04-06-2005, 06:23 PM
Thanks for the suggestions. I'll recheck the fuel filters and screens. I'll post back when I have a chance to do the conversion and get back on the water.
Bruce- "loping"...that sounds like what I may be experiencing. It's really odd because it's so inconsistent. Sometimes the boat idles just great, then the next time I come down to idle it starts surging again... and neither problem is an issue until the boat has warmed up. I'll also add that starting is not really a problem. Even if it dies during acceleration or I kill it while it's surging, it usually starts back up no problem.
Thanks again, Ty.
Like everybody said, sure sounds like a fuel issue. Definitely start with the easy stuff. Open up your gas tank and check for debris, condensation (water)... Then work your way up through the screens and filters to the carb. I would blow out the fuel line (I like to eliminate the easy to check things even if they are a remote chance). As Doug pointed out, the small screen in the carb at the end of the fuel line is called out as an annual cleaning item in the maintenance manual. After that it is fun time with the carb :rant:
04-06-2005, 08:36 PM
The fact that you are experiencing hesitation during accelleration points to the carb. maybe the powervalve is bad. A renew kit from holley (got mine from skidim) will come with a new one and also all new gaskets, needle and seat valves, ect. This would be a great idea. As far as the loping, you should also check your fuel pump. The vent tube coming from the top of the pump leading to the carb. If drops of fuel are travelling through the tube, its bad, and will cause loping and rough idle. I had a boat in the past that did the same thing. Also check your float levels, if the boat is rocking in the lake, with too much gas in the bowls, it will pour out into the intake doing the same thing. This would usually flood the boat making it hard to start after a period of floating and the the boat rocking without the engine running. Like was stated earlier, a vaccum leak somewhere in the intake system would definetely cause similar symptons. The ignition is the best money you will spend. Hope this was some help, good luck. I just rebuilt my carb, it wasn't that hard, took about 2 hrs., but if you don't feel comfortable, and don't mind spending the money, take it to a professional.
04-06-2005, 11:27 PM
Wow! Thought you had my boat there for a minute. Our 93 PS 190 did the same thing. We had to put a new carb on it and the entire problem went away. Just my 2 :twocents:
04-07-2005, 07:26 AM
Like everyone has said on this board - sounds like a carb problem. Rebuild it. It's not hard. I'm no carb expert, the first time I saw one in pieces was when I rebuilt one on my old boat.
I also strongly recommend the electronic ignition... BUT - wait till you have your current problems fixed first. The conversions Rarely go bad - but every now & then I hear of one with trouble. It would really stink to not know if it was your conversion, or the carb that was causing the troubles.
Good luck - the folks on this site are top-notch and can answer ANY question.
04-07-2005, 10:36 AM
Another thing to check out on your carb. In the early 80's, the marine Holley carbs used special float bowl bolts where the bolt shank was a coiled spring instead of a solid steel shank. I think the idea was to maintain a certain amount of clamp up on the float bowl gaskets when the gaskets shrink over time (mostly from drying out in the off season).
Anyway, the bolts (springs) apparantly loose their clamp up tension over time and allow air to pass into the metering block on the carb causing exactly the symptoms you describe. This happened to me several years ago on my '83. It drove me crazy; rebuilt the carb, new manifold gaskets, points, plugs, timing, fuel filters, etc., all to no avail.
The fix was to get a set of standard Holley (solid steel shank) bolts for the primary float bowl (here are four of them on the carb) at the local auto parts store and replace the original primary float bowl bolts with the new ones. It worked for me!!!! Check to make sure the bolts are tight and not leaking a couple time a year and you should be good to go.
04-11-2005, 09:12 PM
thanks again everyone for the input.
well, I installed the new electronic ignition alonmg with a new coil. surging problem is still there, so i'm taking the carb to a local MC specialist...Bennet's in Maryville, TN. I understand he used to work at the factory back in the 80's and he seems like a good guy from our phone conversations.
I wanted to ask a question about the electronic ignition. I found a pink and red wire attached to the resistor when I was getting ready to splice the wire coming from the coil and bypass the resistor. I think these wires have to do with a way for the old ignition to send all 12 volts during cranking because they were both connected to the same pole of the resistor. I think with this new electronic ignition I no longer need these, but I left'em anyway. You may notice I just used the resistor pole as the connection instead of splicing.
One good thing that came from the test run was the discovery of my leak. Late last year we started using the bilge more frequently. I was convinced it was coming from the swim platform anchors. Well, yesterday I noticed water slowly building underneath the engine WHILE TESTING IT IN THE DRIVEWAY!!! Not very likely a problem with the swim platform. After checking all the hoses...then exhaust....aha
I'll post back after I get the carb back on and have a chance to get her out. Here's a glamor shot of my baby. Thanks again for the input, Ty.
04-17-2005, 11:08 AM
problem solved. Donnie Bennet at Bennet's marine rebuilt the carb. He said along with deteriorated gaskets someone had incorrectly installed a 50 cc fuel pump accelerator...should've been 30 cc. I'm not sure when this may have happened, likely years and years ago but the boat ran fantastic yesterday after a few minor tweaks. Bennet's is a pleasure to deal with. and so is Vince at DIM.
Bruce, mine has the solid shank bolts. My lower gasket needed to be replaced though. I think my problems were a combo of the carb, air getting by the lower gasket, and incorrect fuel pump accelerator.