SoCal Jet Boats

Tech Talk => Engine Mechanical / Electrical => Topic started by: RTriebess on July 05, 2009, 01:37:44 PM

Title: engine lays over at 5k rpms
Post by: RTriebess on July 05, 2009, 01:37:44 PM: well I have been fighting the tune on my motor all year. I have been jetting the heck out of it all over the board to find out that my dist. was broken and advance that i thought was locked out wasn't intermitently. got that fixed and it now is running ok I can actualy drive around the lake now.

blown 540 afr 345 heads deamon 850 blower carbs 716 solid roller cam 5lbs of boost
88 jets in primarys 96 in sec boost ref power valves (4.5) timming locked at 28 deg.
37 squirters primary 31 sec. no intercooler
symptoms: pops through carbs sometimes when i punch it like a lean pop and at 5000 rpms it lays over like it is out of gas and if you stay in it it comes and goes it will start excellerating again then lay over then excell again.seams like when it starts making boost is when it starts to lay over.

fuel system:aeromotive a1000 with there filter and bypass reg. 7lbs of fuel psi all the time. have the hard line fuel kit on the carbs

any ideas. to little jet? not enough timing? to much jet? Have went down to 82 prim 85 sec jettting and it would lean pop bad
went back to the 88-96. The plugs are black as if it was rich but it pops like it is lean.
Title: Re: engine lays over at 5k rpms
Post by: Beaveretriever on July 05, 2009, 01:47:43 PM: to me it almost sounds like bad ignition, like the coil, when the motor comes on load if the coil is bad it wont fire. the plugs could also be to cold, like the style of plug doesnt get hot enough to run the motor. so if you give it to much timing to heat up the plugs the motor will knock and not enough timing will make the plugs run cool which would make them black. i know that in turbo cars that we run with carbs, we have had to do alot of work to the carb to allow fuel to run thru the carb like it should. the problem that we have had with fuel is that the boost will create a vacume in the jet area and will basiclly lock up the fuel, but when you layoff the throttle a little bit the vacume in the carb goes away an allows fuel to flow which would give you the accelaration again. i would also check the flot levels because at that rpm you might be starving the float bowls. the jets might be to big on the primarys is why the plugs are black and the motor leans out on the big end. thats just my .02. i have done alot of motor work on big horsepower volkswagen motors with turbos.

the beav
Title: Re: engine lays over at 5k rpms
Post by: GT Jets on July 05, 2009, 02:19:03 PM: What is the plug gap and how much boost?, the higher the CR or static compression, the harder it is to keep the plugs lit, try dropping the plug gap and maybe go one step hotter.

I agree that is is ignition if the fuel pressure is stable. Most of the time the spark is not hot enough to stay lit under boost.......That being said, if not boost referenced it will kick your ass trying to tune.

Also, I didn't see any pics :thumbdown: ;D

GT
Title: Re: engine lays over at 5k rpms
Post by: HDriderTH on July 05, 2009, 04:53:33 PM: I run a 460 chev w/ a 671 10% over and two 1050 Doms. I went from a Mallory Sprintmag to an MSD Promag and had to go up from #93s squared to #99s. I run 34* but dont know how accurate timing marks are, plugs say it wants a little more timing and are coco brown. Plug gap is .018-.020. Hope that helps somehow.
Title: Re: engine lays over at 5k rpms
Post by: RTriebess on July 05, 2009, 05:50:26 PM: spark plugs are ngk r5671a-9 gap at .35
the ignition system is all new msd with box and coil

I will try a smaller gap
the carbs are boost ref power valves demon blower carbs.
static compression is 8.5:1 5% over drive on a 871 blower the highest boost reading i have seen is 5 lbs.
Title: Re: engine lays over at 5k rpms
Post by: GT Jets on July 05, 2009, 05:58:37 PM: Quote from: RTriebess on July 05, 2009, 05:50:26 PM
spark plugs are ngk r5671a-9 gap at .35
the ignition system is all new msd with box and coil

I will try a smaller gap
the carbs are boost ref power valves demon blower carbs.
static compression is 8.5:1 5% over drive on a 871 blower the highest boost reading i have seen is 5 lbs.

Sounds to me like you should gap the plugs at around .025" and see where you end up. ;)..FWIW the -9 in the model number is the gap in mm. :thumbup:

GT
Title: Re: engine lays over at 5k rpms
Post by: crewchief22 on July 05, 2009, 07:06:12 PM: Quote from: GT Jets on July 05, 2009, 05:58:37 PM
FWIW the -9 in the model number is the gap in mm.

GT

??? 9 mm = .354 ???

Some ting wong ;D
Title: Re: engine lays over at 5k rpms
Post by: GT Jets on July 05, 2009, 07:10:26 PM: Quote from: crewchief22 on July 05, 2009, 07:06:12 PM
??? 9 mm = .354 ???

Some ting wong ;D

Not weally ;D, try .9 MM.................hint= .0354" :thumbup:

GT
Title: Re: engine lays over at 5k rpms
Post by: crewchief22 on July 05, 2009, 07:24:44 PM: Damn decimal points ;)
Title: Re: engine lays over at 5k rpms
Post by: countryboyaustin on July 05, 2009, 08:06:29 PM: I have a 1974 eliminator with a bbc. I am running a holley 750 vac second and my boat did this when I tried to run a hei Dist. When I went back with the original Mallory points distributor it quit and ran just fine. I did not figure out what was causing it exactly but I know it was the hei and the points dist doesn't do it!
Title: Re: engine lays over at 5k rpms
Post by: beerjet on July 05, 2009, 10:19:16 PM: I dont think there is enough timing .
I'd start with 34 as Terry stated .

-beerjet-
Title: Re: engine lays over at 5k rpms
Post by: IRRebel on July 05, 2009, 10:43:53 PM: Quote from: beerjet on July 05, 2009, 10:19:16 PM
I dont think there is enough timing .
I'd start with 34 as Terry stated .

-beerjet-

X2. Blown engines are a totally different animal than norm. Normal schools of thought kinda go out the window. I'd be PM'ing Terry on this if it were me. But the advice on the timing, plug gaps and jetting are probably priceless information.

And I'll save Terry saying it.......Put a Mag on it...............

Ray
Title: Re: engine lays over at 5k rpms
Post by: HDriderTH on July 06, 2009, 08:25:08 AM: 34 is alot for blower motors but like I said I dont know how accurate the timing marks are. I think it was set by Phil Stock but dont know. I dont know if you guys caught it on Toms blower build when Josh was degreeing the cam his pointer was 8* off.....they usually are. Was it Ralph last year that was chasing his balencer ring around, kept moving?
Title: Re: engine lays over at 5k rpms
Post by: walshmotorsports on July 06, 2009, 02:21:58 PM: You might want to think about pulling the motor and take it to a dyno. Not just for the hp/torque number but I had a 468 w/871 , 2 850's full roller deal and a mag in my last v-drive cruiser. I took it to the dyno and not just for the hp numbers but the tuning that is avail. I had 4 1/2 years of trouble free 6400 rpm in 3rd (turbo 400) 109 mph w/gps. You could ski inner tube and the back of my boat was always clean, no black fuel or fuel smell behind the boat.
I don't work for a dyno co. I just believe a 3 day river trip costs about the same as a dyno day approx$500 and you should have many trouble free trips.
Last I know there is a lot of guys that can give you great tuning tips I just like knowing my motor is happy rinning at it's peak.
Good luck have a blast this summer!
Title: Re: engine lays over at 5k rpms
Post by: just squirtin on July 08, 2009, 04:11:12 PM: motor pics
Title: Re: engine lays over at 5k rpms
Post by: Fixitall909 on July 10, 2009, 05:33:33 PM: All the pro's I know say A Demon will rob ya on high end everytime!They look really good,but i've never seen one run worth a damn.Just sayin!
Title: Re: engine lays over at 5k rpms
Post by: just squirtin on July 11, 2009, 08:41:51 PM: my demon run damn fine=850 on a bbf
Title: Re: engine lays over at 5k rpms
Post by: electrowoman on July 17, 2009, 07:49:56 AM: How did you figure it out? I'm betting points and retime will cure the problem.
Title: Re: engine lays over at 5k rpms
Post by: walshmotorsports on July 21, 2009, 09:30:39 AM: Fixed yet?
Title: Re: engine lays over at 5k rpms
Post by: RTriebess on August 17, 2009, 10:46:01 PM: well it has been a while I lost my pump the next time out have a donor pump in it to finish out the summer.
when back out after closing plug gap. still did it switched to hotter plug still did it. put the a/f sensor back in and found it going way lean. added jet till I got to 96 99 and a power valve in the sec. got better but still layed over. took it home and tore the top end off and found blower gasket not sealing.found fuel in the side chambers of the intake. Put new gaskets in it and got it refired today. will be back on the water later this week but am pretty sue that that is the problem. I went back to 88 96 for jets and no power valve in the sec.keeping the hotter plug in it.
Title: Re: engine lays over at 5k rpms
Post by: HDriderTH on August 18, 2009, 09:49:01 AM: I'm getting ready to take a look at my base gasket too. I'm running #99s squared, no power valves in two 1050's and plugs are running clean. Thot 99s were awfull big when I got it, worked down to 93s. Then when I changed from a Mallory Sprint Mag to an MSD ProMag The plugs got really clean and had a big "blast area" on them around the arc point so I went back to the 99s. I recently blew out the rubber on my popoff valve, had a 1/4" bead around it to seal. When it does backfire (when I run outta gas) I think I see a puff comming out the side, dunno. When I put the new popoff valve on I set the springs looser, damn thing has four springs on it, inners and outters, they look like valve springs. Hopfully that will take some of the pressure off things. I dont think I've ever been over five grand so I dont know what it does up there.
Title: Re: engine lays over at 5k rpms
Post by: countryboyaustin on August 21, 2009, 12:23:36 AM: like I said mine did this exact thing and when I went back with a regular old school points distributor it runs just fine. I still do not know why But I know it runs well again