AQ271C Fouling Plugs

"I have a problem w/ a 1989 Im

"I have a problem w/ a 1989 Imperial Rappalo boat with a volvo penta AQ271c (350).
Originally I had a 715 Holley 4 Barrel which I down sized to a 600 marine carb. When I troll with this boat it fowls plugs and carbons so much that when I attempt to clear the fowling the lake covers w/carbon. I changed plugs (many many times), wires cap and rotor and water/gas serperator (basic tune up) but still fowl after 4 or more hours of trolling. I was wondering if there is anything else I could do. Some people say the coil could be bad, but I was also told by others that it would not run at all ?
others mention ignition modules (I don't even know where this is) could the ignition be an issue. After trolling but will not plane, top speed is reduced to around 10-20mph unless plugs clear which may or may not happen with in 5 miles of travel.

The boat runs good w/fresh plugs, but the rpm tach never goes over 3900, I believe it should be around 4400 to 4600, it has a duo prop and top speed of 37mph, I understand that it's around 26' boat but given my friends boats are close to same footage and weight, they are in the low 40's w/single props. Shouldn't this boat be more like 45mph? Props are in perfect condition.

Any help is appreciated,

89Imperial"

"Regarding the plugs fouling,

"Regarding the plugs fouling, my first thought is that either the idle mixture is too rich or you need hotter spark plugs for trolling for so many hours in a row. I also have a 350 with a 4-barrel Holley, but I utilize a 9.9 Yamaha 4-stroke outboard for trolling.

My other thought is that your prop is now too large for your engine. It may have been OK when you had the larger carb, but it seems that your engine does not give anymore the original 270 HP since you went to a smaller carb. This is probably why you don't reach full RPM anymore."

"I agree on the 9.9 yamaha, th

"I agree on the 9.9 yamaha, this would solve all the trolling problems, this will hopefully happen next season (budget pending).

As far as the speed vs rpm, this was almost identical to the original carb, even after I had a complete carb rebuild. Could this come down to a coil or ignition for limiting the rpm?

Thanks,

Marty"

First of all get Your props on

First of all get Your props one size down and secondly which plugs are You using. Best plugs are Champion RV15YC4 particularly if You do a lot of trolling.

"I orginally started w/ RV15YC

"I orginally started w/ RV15YC4, but then switched to Delco, then NGK, and now the Delco Marine, I have not run the champions since the new carb, which I might try, but I still have 8 new marine plugs to use up, these will probably fowl next time out, so I will then go back to the champions. The Prop resizing is what I know need to consider, I currently don't know what size props I have because I purchased the boat this spring and did not consider this being part to the problem. I also have two spares that I will check, maybe these are the orginal props and the ones on there now are from someones prior experiment?
Thanks
Marty."