Newbie Needs Mod Advice

qahqn8

New member
Hey guys –

I was hoping folks with more experience could help me think through a few things. I want to build a mud motor for a small boat that I will have to load/unload from a pickup bed by myself, so complete motor weight is key. The boat is rated for up to 10hp but the transom weight restriction won’t allow for the predator 420cc, so I really am stuck with the 212cc. I was hoping some of you could educate me on if I can get ~10hp out of a predator 212cc without having to mill heads, change cams, etc. Also, given that this rig is going to be taking me into some very remote locations reliability and longevity are my biggest concerns.

From what I’ve read, here are the first steps:

1). The mud motor’s prop shaft shouldn’t turn over 4500rpms. From what I have read I can adjust the throttle screw to hit around 4500 rpms without having to remove the governor. Is this correct? Would I need a billet flywheel at this level?

2). K&N style air intake.

3). Robertson’s torque tube exhaust.

4). Rejet carb at around 36-38, 140 emulsion tube. I’ve read the mikuni’s are great but you have to run an inline fuel pump. Not planning on having battery on the boat so the mikuni is out.

5). Upgrade to a decent spark plug, gap at 25.

6). Thinking about 18lb valve springs given floating valve issues but am concerned about this beating up the stock cam and lifters. Anybody have advice/info?

7). Also thinking about the 8 degree timing advance but have heard some folks have had issues with the aftermarket timing keys shearing apart. Anyone have experience with this? Does is even do anything with a stock cam?

Has anyone out there done similar mods on this motor and put it on a dyno?

What other beginner mods have I missed? Like I said, not trying to make 20hp but I need more than 6.5! Thank you all so much!
 
Whats your mechanical expertise ?
Gear/chain drive or straight to the shaft ?
Is the 301 too heavy ?
Spark gap should be closer too .030 .
8*key is too much . 4* imho is going to better suit the situation .
Cam change or ratio rockers . to get the 10 hp , no 18 lb springs .
Bored carb would help .
 
Whats your mechanical expertise ?
Gear/chain drive or straight to the shaft ?
Is the 301 too heavy ?
Spark gap should be closer too .030 .
8*key is too much . 4* imho is going to better suit the situation .
Cam change or ratio rockers . to get the 10 hp , no 18 lb springs .
Bored carb would help .


Thanks for the reply! I've rebuilt some simpler old military generator engines but I'm definitely no hardcore gear head.

In answer to your questions its a straight shaft
301 with the 301 mud motor kit is too heavy
What cam would you suggest for this application? Would I need to upgrade valves/push rods/connecting rods as well?
You're the second person to suggest 4* advance over 8* for this build, gonna follow that advice!
Why no 18lb springs (just curious)?

Thanks so much for your help. This forum is awesome.
 
"Compression is the Holy Grail". "Don't forget", you may, and this is only a suggestion, possibly need higher octane fuel. Please be careful; Don't go overboard with the octane.
 
Nothing outrageous as too cam the cl-1 is drop in and a bored carb from Dover power with exhaust and air cleaner should get you close .
I might even leave the flywheel alone .
Reinforcing the transom with the bigger engine might be better .
Icant say which ways better the reliability shouldnt be a concern . Boat ends up heavy the more you toss in . I thtink the 301 .
 
Nothing outrageous as too cam the cl-1 is drop in and a bored carb from Dover power with exhaust and air cleaner should get you close .
I might even leave the flywheel alone .
Reinforcing the transom with the bigger engine might be better .
Icant say which ways better the reliability shouldnt be a concern . Boat ends up heavy the more you toss in . I thtink the 301 .

Thanks for the parts suggestions, I'll definitely look into them. Havent heard of the Dover carb yet. Im going to try and adjust the throttle to get 4200-4500rpms and leave the gov on. from what ive read most guys just leave the stock flywheel until 5000rpm, that sounds about right?

A 301 would for sure be easier but now I'm back to looking at weight differences hahaha. Between the bigger motor and larger kit im looking at another 35lbs of weight.

I think I'd rather spend some time building up the 212 instead of lifting a 120lb complete motor out of a truck.

Seriously appreciate all the help. This is good info
 
Dover power online .
He has ready too go as well . Maybe not with a governor though .
Be worth a phone call excellent people with solid advice .
In fact i would definatly call 704-485-2020
 
Everyone who is hot rodding these takes out the gov.

Aftermarket air filter
big pipe
cam
flywheel key

That should get pretty close. Guys are running the stock flywheels up to 6500 that I know of personally. You sound like you are concentrating on torque not wanting to go above 4500rpm. Its way more fun to make a 20pd engine go 10hp than a 120pd

Did you buy one yet? If not for your app I would think the hemi would be better
 
You could run the cheap tach off amazon they are about 25bucks just wraps around the plug wire and vary throttle to keep it under the RPM you want.
 
4). Rejet carb at around 36-38, 140 emulsion tube. I’ve read the mikuni’s are great but you have to run an inline fuel pump. Not planning on having battery on the boat so the mikuni is out.

Fuel pumps that are used are pulse pumps that run off vacuum. Hardest part is figuring out where to pull the vacuum from, manifold, valve cover side of the block are all spots that i have seen used. Simple drill, tap and insert nipple good to go.
 
Briggs had a standard outboard style with the vertical animal/intek .engine .
Wonder how a conversion of old out board would work ? No need to pump water , would be a pluse .
 
Back
Top