Other JM781 set up discussion

N3vrSat1sfied

N3vrSat1sfied

Military Member
Location
Fort Worth, TX
Jet Maniac 781 set up

Seems like more and more people are running these motors, the majority seem to be running the recommended 38's. I know a few of us have oem 44's just thought maybe we can post our opinions and thoughts here.
 
wanderer1

wanderer1

Location
Cruising Around
I have TBM's and Zero's,both work well,huge price difference though. I now you are talking about 38's and 44's but what about 46's? Had great results with the Mikuni 46 from 718 up to 885. I really prefer them over the 44 and no ? when compared to 38's. You do tend to use more fuel but hey.
 
N3vrSat1sfied

N3vrSat1sfied

Military Member
Location
Fort Worth, TX
wanderer1 said:
I have TBM's and Zero's,both work well,huge price difference though. I now you are talking about 38's and 44's but what about 46's? Had great results with the Mikuni 46 from 718 up to 885. I really prefer them over the 44 and no ? when compared to 38's. You do tend to use more fuel but hey.
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noticeable difference between flywheels?

good point, I have not ran into any one running 46s, other than a picture I saw an hour ago with 46s on a jm 781. maybe he can chime in.
 
wanderer1

wanderer1

Location
Cruising Around
Difference in flywheels felt in wallet IMO. Probably get flamed for saying this but it is only an opinion, wasting time with a ported 781 and running 38's and the 46's always feel better to me than the 44's I've had. No expert here,just tried different stuff and really like the 46's. Put a 2 barrel on your 396 or dual Barry Grants?
 
N3vrSat1sfied

N3vrSat1sfied

Military Member
Location
Fort Worth, TX
wanderer1 said:
Difference in flywheels felt in wallet IMO. Probably get flamed for saying this but it is only an opinion, wasting time with a ported 781 and running 38's and the 46's always feel better to me than the 44's I've had. No expert here,just tried different stuff and really like the 46's. Put a 2 barrel on your 396 or dual Barry Grants?
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thanks for the input, I have always thought that JM and Blue were going more for a budget thing with the 38's. But I agree it seems like not enough carb for that motor when a stock 760 comes with 44s, but they are the engine builders not me! Which is why we have this thread to figure out what works best.
 
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mxmat813

mxmat813

Location
Groton, NY
Not a JM781 but I'm running a Northwest Sleeve ported by Watcon @86MM (789). Running dual 38's, #Zero flywheel, B-Pipe and enhancer. Haven't got a great chance to judge set up yet because I had water intrusion on one cylinder but the other side plug reading came out spot on. 132.5 High, 77.5 Low, 2.0 Needle, 95G spring. Seems to go through much more fuel than my 701, hopefully it has something to do with the water intrusion?? Only getting about 25 mins out of a Kart tank.
 
SXR141

SXR141

Location
northern illinois
Rickter fs1 with a JM BB motor (86 mm) with 38's and seems to run good to me I'm no expert either but what I've been told 38's are very efficient carbs. I've talked to a couple different engine builders and their advice to me was going up to 44's wouldn't really be worth the small performance gain you would get for how much more fuel you would go through with 44's.
 
naticen

naticen

Site Supporter
Location
wilmington, nc
Dang. I just ordered a couple 38's because that was recommended. My 787 xp is 110 horses and will drink several gallons in an hour through a couple 40's. I guess that's I series carbs with rotary and power valves but man. I really want my mpg's but i don't want to feel like I'm throwing away power. Maybe have them taper bored or fit some 40 I's for a compromise?
 
CWAmeden

CWAmeden

Location
Mill Creek
I'm running jetworks modded 38's and it runs really good with these. Chris said he's tested with bigger carbs and likes the 38's the best. I was going to go bigger but I trust him so am sticking with the 38's.

Sent from my SCH-I535 using Tapatalk 2
 
subhard

subhard

TITS OR GTFO
Location
anchorage ak
Is there a big difference between oem 38s and blackjack 38s? My new 760 is coming with BJ 38s and I was wondering if they'll work better than the oem 44s that usually come with it.
 
swapmeet

swapmeet

Brotastic
Location
Arlington TX
SXR141 said:
Rickter fs1 with a JM BB motor (86 mm) with 38's and seems to run good to me I'm no expert either but what I've been told 38's are very efficient carbs. I've talked to a couple different engine builders and their advice to me was going up to 44's wouldn't really be worth the small performance gain you would get for how much more fuel you would go through with 44's.
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CWAmeden said:
I'm running jetworks modded 38's and it runs really good with these. Chris said he's tested with bigger carbs and likes the 38's the best. I was going to go bigger but I trust him so am sticking with the 38's.
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This and this...^^^

I'm running the JM781, TBM, dual 38's set up by Chris and Factory pipe Limited Chamber. I asked Chris a lot of questions when building my motor and one was about the 38's vs. 44's. He said the same thing as above, 'We've tested it the power difference doesn't justify the additional fuel you'll consume.' If I was running a full size tank, i'd consider bigger carbs to try out, see how it hits. Also I hate hate hate tuning carbs, so i'm not inclined to change from what works well.

I can go forever (thats what she said) with a cart tank on these 38's in my Chan. I start to chase a boat and head back to shore because I don't want to run out. Pop my hood and I have half a tank!

Basically, until I have the cheese for a 900+ motor, my JM runs awesome on 38s, so why mess with it.
 
stagesrt4

stagesrt4

see ya out there
Site Supporter
Location
St Charles IL
^^good info

Yea i plan to stick to the 38s for now...bigger carbs n bigger pump will come once i go to 898.

Ill be running race gas with my setup
 
SXR141

SXR141

Location
northern illinois
There's a few different skis in our group and the one with a riva ported 718 with 44's goes through wayyyy more fuel then any of us. And that's comparing to motors that are more cc then the 718 but we have 38's still.
 
96superjet

96superjet

Location
Home of the Steelers!
I'm not going to get into the whole "uses more gas" discussion. Instead I'm gonna weigh in on the JetManiac 781 Big Bore with other than stock 38mm carbs.

After my JM781 showed up, I stole a set of Mikuni 44mm SBN carbs and Pro-Tec intake manifold off a 96 Blaster I had sitting around. Chris (JetManiac) provided me with the following carb settings :

Main Jet = 110 H
Pilot Jet = 125 L
Needle/Seat = 2.3
Spring = 95
Pilot screw = adj 3/4 turn out
Main Screw = adj 1.25 turn out

It was pretty blubbery on the low end, so I started adjusting the screws. I'm currently at 3/4 turn out on both Lows and Highs. Cleaned it up a bit, but still not good enough. I'm ordering a set of 122.5 and 120 Pilot jets to see if that helps to clean up the low end. I'll update this when they arrive, I have them installed and tested.

My setup is as follows:

Gas Octane = 93
Altitude = sea level
Motor type/setup = bb781 61x/62t, 185 psi, 38cc domes, b pipe w/ mod chamber, MSD enhancer, #ZERO lightened flywheel, Pro-Tec intake manifold and Mikuni 44mm SBN carbs

MikuniSBN44Jets.jpgMikuniSBN44s03.jpgJetManicBigBore1.jpgMikuniSBN44s.jpg
 
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