62t RN build advice

[jotab]

Hi! I am finally getting around to replacing the engine in my RN. Last engine (6m6, with a 750sx intake flange welded on by the previous owner) had a bad crank and tore a rod, smashed a hole in the crankcase, kept running on one cylinder for a while until finally properly locking up. So more or less a total write off.

As I am located in Sweden where the stand-up market is very small, parts are few and hard to come by, so I want to try and work with what I have. There are also no machine shops with knowledge about these engines that I know of.

I have the following parts at my disposal

• Stock 62t short block from ebay with ~150psi in each cylinder
• Dual 46mm carbs with intake and stock reeds
• Factory B pipe
• Ada girdled head (one of few parts which can be salvaged from the old engine if I select to buy a new dome for the affected cylinder)
• MSD ignition (CDI and coil)
• Factory flywheel/stator
• Aluminum waterbox of unknown brand which sits next to the battery

The aim of the build is to have something that is mainly reliable, but with adequate power. I am not doing backflips, more some light wave jumping and general riding, but more power equals more un!

My idea was to use the 46mm carbs, b pipe, aluminum waterbox and msd ignition on the stock short block, together with the stock flywheel and stator. For this I have some questions;

• I am thinking that 46mm carbs is a bit extreme, but as that is what I have available, I would prefer to stick with them. Any opinions here? Would it be necessary to tap a second pulse fitting? Any recommendations on jetting?
• Is it worth it to buy a new (or two) dome(s) for the girdled head? Which size? Remember that shipping and taxes will probably at least double the price.
• How would you route the cooling if using the stock head? The ada head? Would you run dual cooling? The waterbox has what looks like a fitting that opens when the pressure is high enough, can provide pictures when at the garage.
• Is there anything else that you would change out? Keeping in mind that parts are double the price when shipping and taxes are paid and shipping usually takes multiple weeks.

Thankful for any input as I have been longing to ride ever since the engine exploded!

 

[fastgtfairlane]

I have basically the same setup you're wanting to build with the exception that I'm running dual 44s instead of 46s. If I did it again, I'd go with 46s for the reason of not having to go bigger if I went bigger on the engine. I've seen 48 full specs on 701s before so dual 46s will be good. You'll just have to get them tuned for your engine.

 

[spinyard]

I would stay with the stock carbs if I were you you can get plenty of power out of them and as soon as you go bigger your fuel range will deplete fast

 

[fastgtfairlane]

Stock carbs are designed for stock engines. Sure they'll work decent on a modified engine, but you're leaving lots of power there. You have to pick one: horsepower or fuel economy.

Op already has dual 46s available, so why not run them?

 

[Sopsurfer]

This is my humble advice. Take it for what it's worth.

1. Get rid of the MSD coil. They generally suck as compared to a genuine OEM unit. The MSD CDI is good. Turn it all the way up and run it.

2. As far as carbs go I've had the best luck with the stock 38s. They give the best low end. I've run others and made considerably involved attempts to get OEM 44s to work well. At the end of the day I was always happier with the 38s and my range was substantially better than any alternative. I run them with open flame arrestors even in surf. The jetting window is generous and they are pretty trouble free.

3. Your small waterbox inlet is for water injection if it's what I'm picturing. I would block it with a pipe plug. I've never run anything to this with a 701. Perhaps others have different results and expertise but it's my experience it's not needed.

4. Dual cooling isn't needed. It's cool but not needed. I plumb for single or dual in the following manner. Pump to manifold. Bottom of head pipe to rear head fitting. Front head fitting to restrictor and stinger. Head pipe fitting straight overboard to the pisser or hot hands. I like the pipe at 3/4 open on top, closed middle, and 3/4 bottom. I run a 1/8 drill in the water jets by hand to make sure they are free of casting slag. There are many ways to plumb but this has provided me the best results.


What year round nose are you building? Bare in mind all my above advice comes from someone who rides surf basically exclusively.