650 swap to 701 tuning questions

[Mouthfulloflake]

I dropped a stock 61x engine in my boat last week, taking the place of the 650 with 185 psi compression.

the 650 was running a carb, jetted for a 701 and B pipe, 120 lo, and 145 hi jet ( from memory)

the 650 ran well with that setup, with a coffman sizzler pipe.

I ran the same carb, and same pipe on the 701 with stock compression, and the bottom almost felt 'mushy'?

is it possible thats too lean for the 701 with a 120 lo jet?

on the mid and top it runs well, makes more power mid and top than the 650, I swear the bottom is 'mushier' though.

does any one have thoughts?

I suck at fine tuning.

 

[marz831]

That jetting should be correct. What pop off?

 

[Mouthfulloflake]

I THINK the spring and N/S were left stock.
what do you recommend?

I had called LPW and wrote it down when I first rejetted the 701 to the sizzler pipe, but I forgot it all now.

edit:

searched an old thread and found it posted there, same issue with the old 650, but it seemed to pull harder quicker.

shiny spring, 1.5 ns, 120 low, 145 high

 

[marz831]

Hmm, I have a similar setup except I am running a single carb on 62t cases. I am using a 2.0 n/s with a 95gm spring. That would give me a lower pop off than you...about 25 psi. You are around 32ish with your current setup.

It's all about trial and error....yeah, it sucks.

 

[accbr]

I ran that pipe on my 701 for awhile and had the same jets, but a 2.0 N/S 95g spring. That's what Paul told me to use. It ran pretty good with no flat spots.

 

[Mouthfulloflake]

Ill upgrade to a 2.0 ns then, and see how that works.

thanks for the info guys.

 

[Mouthfulloflake]

I noticed also, there is the white milky stuff in the carb, ive heard that was caused by poor reed sealing?

would a bad reed sealing lip make the bottom end muddy?

keep in mind the mid and top are very strong.

 

[Matt_E]

Possible. I'd fix it, to be sure.

 

[crammit442]

I noticed also, there is the white milky stuff in the carb, ive heard that was caused by poor reed sealing?

would a bad reed sealing lip make the bottom end muddy?

keep in mind the mid and top are very strong.

White milky stuff is fuel/oil/water emulsion.

 

[Mouthfulloflake]

right, but ive read that its a sign of bad reeds.

It seems odd it would hang around on the sides of the carb? wouldnt it get sucked in?

is there any sign of poorly sealing reeds then that you are aware of?

Id hate to tear into it, and find all reeds sealing well.

My hood liner leaks alot, so there is always water in there... I was thnking maybe the erratic pulses of the non-sealing reed(s) could suspend some of that watery/oily milky goo in the carb throat?

I appreciate your thoughts!

[ I was hoping to see allgood yesterday, to have him ride it, its stronger than his... hehe]

White milky stuff is fuel/oil/water emulsion.

 

[Matt_E]

Signs of poorly sealing reeds:

Smoke out the carb
Visible fuel mist coming back out of the carb
White emulsion mix (if you got water around the carb, as I frequently do.)

 

[Mouthfulloflake]

ok.

I havent watched it while running.
so I cant speak on the mist or smoke out of carb I will check that though.

my boat takes on a TON of water, so there is always this, blip.blip.blip dry the hull/carb out series after anything involving being IN the water.

so, maybe the reads are ok, and im simply lean on the bottom due to the 1.5 NS instead of the 2.0?

I hate tuning at this level.

 

[Matt_E]

You really should be running a 2.0

 

[kevbo]

Your engine should almost fourcycle at 1/4 throttle for best responce. A 2.0 needle with an 80-95g spring is normally good pop-off for stock cyl standups. Check your ignition timing, it will affect the pilot jet and pop-off requirements. Try to make it noticably rich at low throttle and clean it up from there.

 

[Mouthfulloflake]

I do not understand what you mean by 4 cycle t 1/4 throttle?

Timing, MSD enhancer, stock lightened flywheel, stator advanced a bit...

dang, I wish I had a tackle box full of jets, needle/seats, and pop off springs.
it would be much easier to tune these things.

Your engine should almost fourcycle at 1/4 throttle for best responce. A 2.0 needle with an 80-95g spring is normally good pop-off for stock cyl standups. Check your ignition timing, it will affect the pilot jet and pop-off requirements. Try to make it noticably rich at low throttle and clean it up from there.

 

[kevbo]

When a two-stroke is too rich it will four-cycle or sputter. They usually need to be doing this some at low throttle in order for the engine to respond quickly when the throttle is snapped open. Its easy to get a feel for setting the mixture in this range with a single 44.