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AIR POWER
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157 Posts
Discussion Starter · #1 ·
I have a 850dp on my 455 olds (rebuilt carb, rebuilt motor). The motor runs good and the spark plugs read right on after running it but when I get into the throttle wide open it has a bog to it, but if I let off and hammer it again it picks up with no bog. I have changed out the secondary jets to larger ones to try to solve teh problem but no luck. I dont know if I need larger discharge nozels or what? Any Advice would be appricated.
 

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Sounds to me like undersized accellerator pumps, did it ever run right under hard accel?, there are pump cams, nozzles, bigger pump bellows, someone on here has a proven recipe...

GT
 

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AIR POWER
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157 Posts
Discussion Starter · #3 ·
No it never did run right on hard eceleration and wot. If anyone has a good setup that I can try for my carb let me know.
 

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850 DP set with 80 pri. with 6.5 PV, 87 sec. 40 CS front and rear no air horn! How does this compare with what you have already? :)devil
 

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E-7 Sheepdog (ret)
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What size accel pumps are in it?

My Holley runs the small on the primary and the large pump on the seccondary. Has always worked perfectly this way.
 

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There is supposed to be a small needle under the squirter screw, if its not there, or its stuck, or it doesnt seat correctly it can cause your problem. Remove the squirter, and see if there is fuel right up to the top of the boss, if not then SLOWLY move the pump arm and see if fuel comes to the top. If it does, see how long it takes for the fuel to go back down, it shouldn't go down at all. These needles wear and get corroded and don't seal. The first pump squirt must refill the passage from the fuel bowl level to the squirter, the second quick shot gets all of the normal squirt before the passage can empty. TIMINATOR
 

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AIR POWER
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157 Posts
Discussion Starter · #7 ·
Well apparently my Holley isn't a 850 I checked the list numer and it's a 4780-2 which makes it a 800. I checked the little needles under the squirters and the rear one was stuck and I had to tap it out. I cleaned the needle up a little and it doesn't stick no more but that doesn't mean it's no good. I have 76 primary jets/6.5 PV, 88 secondary jets, and both front and rear squirters are 31.Any thing else I need to check out or replace??
 

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Jet boat service
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Tapped Out I assume that your timing is correct. If the changes you made to your carb did not solve the problem , I'd also check the manifold vacumn numbers on your new motor. You may need to finish the tune with a power valve change. The transition circuit may coming on be a bit late. For example, if your motor is making 14 " of vacumn at idle you may want to try an 8.5 PV. If you still have a problem I'd look at the fuel pressure during the W.O.T stumble. Good luck. Jim
 

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Sit N' Spin
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1,423 Posts
Tapped Out I assume that your timing is correct. If the changes you made to your carb did not solve the problem , I'd also check the manifold vacumn numbers on your new motor. You may need to finish the tune with a power valve change. The transition circuit may coming on be a bit late. For example, if your motor is making 14 " of vacumn at idle you may want to try an 8.5 PV. If you still have a problem I'd look at the fuel pressure during the W.O.T stumble. Good luck. Jim
Good to see ya posting here Jim.
 

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AIR POWER
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157 Posts
Discussion Starter · #10 ·
This carb has the 30cc prim. and 50cc sec. accelerator pumps. I think I have narrowed the problem down to the stuck needle under the squirters. Does anyone know if the numbers for my squirters sound correct?
 

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Sit N' Spin
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Yes, your carb came stock with 0.031" squirters in both the primary and the secondary.
 

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Angry American
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This carb has the 30cc prim. and 50cc sec. accelerator pumps. I think I have narrowed the problem down to the stuck needle under the squirters. Does anyone know if the numbers for my squirters sound correct?
here's a link to the Holley Carb Numerical Listing to give you all the factory specs on Holley carbs.
http://www.holley.com/data/TechService/Technical/Carb Numerical Listing.pdf

it can be a little confusing when you first look at it. The way it works is the odd number pages as they come up have the list numbers of the carbs and some info. The even numbered pages are a continuation of the info of each carb along the corresponding line.
For example, your carb is on page 5 line 5. The rest of the info is on page 6 line 5. Hope it helps
 

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E-7 Sheepdog (ret)
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6,834 Posts
This carb has the 30cc prim. and 50cc sec. accelerator pumps. I think I have narrowed the problem down to the stuck needle under the squirters. Does anyone know if the numbers for my squirters sound correct?
With that seal un-stuck, I'll bet it works fine now.

Holley does say that any idle vac. over 12" (ie, 14"), a 6.5 pv is plenty, no need to go higher, but only your testing is for certain.

Below 12", go 1/2 of the vac. figure.
 

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Sit N' Spin
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1,423 Posts
With that seal un-stuck, I'll bet it works fine now.

Holley does say that any idle vac. over 12" (ie, 14"), a 6.5 pv is plenty, no need to go higher, but only your testing is for certain.

Below 12", go 1/2 of the vac. figure.
Yeah but seriously, does Holley even know anything about jet boats? :D :D :D
 

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E-7 Sheepdog (ret)
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You know they know more than SOME people you & I know know, you know? ;)

Ah the memories.................. :)sphss

Live From New York, It's Saturday Night!". :D
 

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Acc pump adjustment

The arm that contacts the pump lever must be set so even the slightest throttle shaft movement creates a squirt. I usually make it contact the arm at rest, but not enough to restrict a full pump charge. Holley has a clearance number in their adjustment notes, I ignore it and make them touch at rest. If you have to "recock" the pump then the squirter needle is allowing a drain back as you've incountered...........Ray
 

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Jet boat service
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126 Posts
There is alot of good info here for sure. When I look for problems like these I check for everything . Squirter size and timing, jetting , power valve selection, carb adjustment, fuel pressures and Engine vac numbers at idle and wide open throttle.
Holleys are great carbs and 95% of the time they are right on the money , out of the box, but cam choices, mainfold choices , engine size and a particular load condition may require changes from the factory set up. Case in point; If you have too much cam and your vac is very low the 6.5 will be dumping fuel when it is not supposed to. I have seen this many times and I have used power valves as low as 2.5 hg ratings. Especially on Jet boats where you have high load conditions at part throttle and low vac numbers. On the other end , in drag racing or circle track racing where loading is very high and a particular motor is maintaining higher vac numbers in the upper RPM range you can have a situation where you will run too lean and you may need an 8.5 Hg PV. I believe that you need to cover all of the bases here. I have one customer that had a 26 ' aluminum fishing boat (heavy) powered by a 350 chevy 300 HP kodiak. Pushing a 3 stage Kodiak Jet. It had a terrible lean bog at mid range. The customer took a vac reading on my suggestion and found that the motor was making 16 Hg at cruise speed. I went to a 10.5 PV , large .035 squiters and 50 cc pump on the secondary and the boat was a different animal. This customer went to numerous shops over the years with no positive results. There are some people, and some books out there that will tell you that this is ridiculous for a small block.. Don't get me wrong here, Books are great and you can read about this in the Holley carb and manifold book by HP books , on page 129 under power valve tuning. Some times you need to just forget about the book and go on experience after testing for all possible solutions. I have been building and tuning Holley and Rodchester carbs for performance engines for over 40 years and can tell you that there are some things that the books or techs can't tell you.
Tapped out says he has a 50 cc secondary pump, if it was me, I would top that off with a .035 secondary long tube squiter. The answer is there and I am sure you will find it. Let us know what solved your problem. Jim
 

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AIR POWER
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157 Posts
Discussion Starter · #20 ·
Thanks to everyone for all the help. The problem was in the secondary needle valve under the squirter, it had some corrosion on it and was just stuck down in the hole. Timinator hit it right on the money, it would of took me awhile to figure it out on my own. I bought new needles and some larger squirters but didn't install the new squirter yet since the needles I installed fixed the problem. I guess I can either try them out to see what happens or just not fix what aint broke. (ready for summer)!!!!
 
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