View Full Version : loss of engine power sometimes...help??

Upper Michigan Prostar190
06-04-2005, 07:44 PM
Last two times out with the boat, I had a couple episodes where the engine "bogs down" a bit. Its like it looses power a bit. IT dont stall, or really cough or anything, just bogs down, then if you give it more gas, it seems to recover. but its getting anoying. The guy I got the boat from said he thinks the boat is due for a Carb rebuild. its a 1991 Prostar. 351 w/powerslot. he did 2 carb rebuilds since it was new. he advised me of doing one when I got it a month ago. I was also thinking about a tune up, plugs, wires, cap, rotor, points, and maybe fuel filter. and the carb kit for a rebuild. It also made a funny muffled pop noise too, almost like a muffled backfire, when it was bogging down, but only twice.

Could this be an ignition/electrical issue? coil perhaps?

Are all these parts availabe at an auto parts store? or are they special Indmar parts?? I assumed since its a 351 I coiuld get them at a regular auto parts store.

ANy other ideas or suggestions?? any reasons this might me happening? I would welcome any help!! Thanks!! :D

06-04-2005, 07:58 PM
Start with the basics, fuel quality and pressure, plugs/cap/rotor/points(get the electronic ignition conversion if it doesn't already have it) timing, and fuel delivery. This last one should go along with a warmed up, dry compression test. If the rings don't provide enough of a seal, you won't have enough fuel drawn into the cylinders.

Before you do anything else, what does the exhaust smell like? Is there a strong gas smell or does it not smell much at all? If the smell is strong gas, you know that the carb may need a rebuild/setup. The other thing that will cause this "pop" is being set too lean. Check the plugs for color and wear. If I bought a boat, the first thing I would do before even taking it out is check everything possible so I would have a basis for its condition. This is generally called a marine survey if it's thorough enough.

Upper Michigan Prostar190
06-04-2005, 08:04 PM
Thanks JimN. :D Where can I get The HEI conversion?? any good places to get one from? or can you just get that at any auto parts store? OH yea, I forgot to add, the boat has only 185 hours on it. Its low hours so I dont know if thats got anything to do with it?

I appreciate any help. Anybody else got any input?

06-04-2005, 08:43 PM
Don't know alot about the carb and such but I did have somewhat of the same problem after i got my 88 tri-star a few years ago. It also made the pop sound. Like you said it sounded like a muffled backfire. I ended up having to have the power valve in the carb replaced. The guy told me that when it backfires alot of the time it damages this part. It was not a costly piece. After he replaced it and tuned the carb my problems went away. :twocents:

06-04-2005, 08:51 PM

Here ya go. It's about a 30 minute job and makes a big difference.

06-04-2005, 11:17 PM
I think we have the same probem where thew bboat boggs down at a higher speed, , but we know that it is the points in the disrtibutor, we are going to put electronice ignition in it soon, you should do the same.

Upper Michigan Prostar190
06-05-2005, 10:52 AM
OK, thanks all! I appreciate the input. and welcome any more that anyone has.
SO, I am going to start with the carb rebuild, tune up, and sounds like I should convert to electronic ignition. I found the carb kit on skidim website for my model carb, the list #is 50469. so I need the 4160 kit and the separate gasket they indicate. so that takes care of the carb kit.
Now how about the electronic ignition conversion? I see they have prestolite and mallory conversions. Can I tell which I have by looking, or do I need to take the cap and rotor off to get inside to see? and if I convert to elctronic ignition, do I have to change coils then??

How bout the fuel filter? I see they have a racor 110 that says its for mastercraft 86- ? would that be the one?? From what I can tell, it looks to me like the fuel filter is near the fuel pump, right before it. is that correct? I was a bit unsure of what fuel filter is correct...... :huh:

how bout plug wires, and plugs, and cap and rotor? should I get those at skidim too? or just get them from a reg auto parts store? or do they have marine application parts for those too?? I see they have tune up kits with most of that stuff. Whats your opnion there?? It looks like that have just about everything I need for a total tune up and carb kit, plus the electronic conversion. It looks like the skidim.com place has all the bases covered.

Does Skidim have technical type help people that can help me order the correct parts? If i tell them what year the boat is, can they help me get all the right parts I need?
Keep in mind, I am not a helpless idiot, but not a mechanic either. I have a friend that's ASE Master certified with his own shop that will be doing all the work. I just want to make sure I order the correct parts.

Once again, thanks alot for the help. :D I truly apppreicate it!!! :wavey:

06-05-2005, 11:16 AM
Call Skidim and tell them the boat you have, briefly explain the problem, and tell them the parts you want. They will be able to get the right setup for you.

They do offer technical help.

06-05-2005, 01:04 PM
How bout the fuel filter? I see they have a racor 110 that says its for mastercraft 86- ? would that be the one?? From what I can tell, it looks to me like the fuel filter is near the fuel pump, right before it. is that correct? I was a bit unsure of what fuel filter is correct...... :huh:

Does Skidim have technical type help people that can help me order the correct parts? If i tell them what year the boat is, can they help me get all the right parts I need?

You have two fuel filters. The Racor 110 is the water seperator, you'll find it if you follow the fuel line back from the pump. If it is the same as mine (it should be) it will be a gold color housing. It will be easier to change that filter if you unbolt the entire water seperator and pull it out from under the engine. The other filter is in a bowl on the bottom of the fuel pump and is held in place with a band that has a bolt on the bottom.

Skidim is great at getting you the parts you'll need and they have decent prices.....They have my business!

06-05-2005, 02:06 PM
They'll ask whether the distributor cap is screw-down or clip-down too, so make note of this. If you can find the engine serial #, they may need that.

When I said take care of the basics, I meant that the compression test, timing and visual inspection should be done first. You may have new parts that don't need replacing in the motor and changing them won't make a difference if the problem lies in setup or the motor's general health. That's the reason for the compression test. If you check the timing and see the timing mark jumping around, that indicated a worn distributor shaft bushing. Another thing a lot of people neglect is the flame arestor. Make sure this is clean. You can use any carb cleaner, clean gas, or brake cleaner. I like the NAPA carb cleaner that evaporates really quickly. It's not particularly friendly to the environment, but neither is running a motor with a clogged flame arrestor.

You may see a sticker with engine specs on one of the valve covers. This will show plug # and gap, timing and dwell(dwell is not adjustible with the electronic conversion kit) and some other details.

BTW, the conversion kit isn't HEI, it just gets rid of the points and their inherent unreliability issues. HEI would require a different distributor and coil, at the very least. Not a bad thing to do, but there are thousands of boats with the standard coil ignition system out there that run just fine.

Upper Michigan Prostar190
06-06-2005, 12:08 PM
Thanks again!! :)
Cool, I put a call into skidim today, left a message and waiting for them to call me back. I am still going to do a tune up, timing, and carb kit, as I know its due for one from what the previous owner told me. I asked my mechanic about the dry compression test, and he said he could do one of those fairly easy. I am also going to have him throw it on his scope once he gets the tune up done, sets timing, and sets the carb. That way he can get it right.

One more thing, are there any technical things like plug gap, or any other settings he needs to know that are unique to these indmar engines?? where do I find these specs? or will skidim.com know them? :confused:

east tx skier
06-06-2005, 12:18 PM
Plug gap ought to be .035 if memory serves.

Upper Michigan Prostar190
06-06-2005, 12:34 PM
Thanks east TX skier! Funny, skidim told me the gap was .018 :confused: SO what should I do, split the difference...? :cool: ;) :purplaugh But seriously, what IS the correct gap?

06-06-2005, 01:23 PM
.035 is the correct answer

06-06-2005, 01:29 PM
I agree, .035 is correct on my '88 351.

Upper Michigan Prostar190
06-06-2005, 02:04 PM
OK, well, the guy at skidim didnt sound completely positive that it was .018, so he sound mistaken then. He didnt sound like he was a techy type, so I hope he got me the right parts. There were just a few parts I was unsure about finding on their site, the fuel filter and the water spearator, but I think he got them correct. and he said I needed 8mm plug wires too. anyway, on teh plug gap, He said he "thought" it was .018 so does anybody else got any votes on this? I take it that .035 seems to be the concensus here.....

06-06-2005, 07:22 PM
.018" is closeer to the points gap, and that's not even right. .035" should do it. As I said in another post, there may be a sticker on one valve cover with tuneup specs. If it's gone, the info will show up here.

06-07-2005, 12:48 AM
I had a problem like that last season. I changed my fuel filter and it ran great today.

Upper Michigan Prostar190
06-08-2005, 02:36 PM
cool. Well, she is at my buddies shop today getting the tune up and carb kit. I will let you all know how it worked out when I get it on the water for a test drive, which I hope is tonite...... :rolleyes:

06-08-2005, 02:49 PM
Hey UP,

On your electronic ignition - I got a Pertronix one and I also got their upgraded coil...works fine - easy install...my distributor has a metal tag on it...Mallory and is bolt down...bear in mind, I've a completely different motor than yours...but similar problems, ha!


Upper Michigan Prostar190
06-10-2005, 10:15 AM
well, heres the deal.

My boat already had the electronic conversion to eliminate points. :eek: so I guess I have a spare module now.

and the tune up seemed to do the trick so far. We skied with it last nite. My mechanic buddy took his scope out in the boat, and also checked the timing. he did his magic setting the carb mixutre, idle, etc.... took a test drive, and then we went skiing for a bit to try it out. All is good so far. :)

Here is a question for you: All the plugs seemed to be in very good shape exept the two rear most plugs on teh engine. The last plug on each side closest the rear of the boat were both like fouled, blakc and charred. why is this?? all other 6 plugs were fine, very fine infact. This may be stupid, but is it because the engine sits tilted in the boat?

all in all, it runs great. his tweaking on the carb really seemd to help out the idle too. it just purrs now.

east tx skier
06-10-2005, 12:07 PM
Good question. First time I pulled the plugs on mine, the rear, portside plug was fouled, but none of the others. Since then, with regular maintenance, haven't had any other fouled plugs.

Upper Michigan Prostar190
06-10-2005, 02:46 PM
Strange hey...? :confused:

06-10-2005, 08:04 PM
The tilt may have something to do with it. The rear cylinders may be getting a bit more gas than the others with the carb set too rich and they fouled. Sounds like you have a winner, I would still check the compression.