manifold filling with gas/low compression

[starsnstripers]

Re: manifold filling with gas/low compression

Thanks bondo - Your right I forgot to open the throttle on the compression test. It's a 4 pt. engine stand, stable enough. Specs on this gm 250 165 hp say compession should be 140 psi. and I have had the dist. out because I manually primed the system with the oil pump because I had a slack lifter which is ok now. With valve cover off set mark on tdc just before the intake starts to open. points at 16* plugs .035 fuel pump line into bucket good strong sguirts. I'm going to try a few things and start over here. New exhaust gasket rebuild carb new plugs they came with the motor anyway. Level engine stand. I will follow up with you guys on my progress. Thanks for all the pointers and suggestions. very appreciated! p.s. great responses

 

[starsnstripers]

Re: manifold filling with gas/low compression

OH ! and of course the rotor towards #1 on cap F.O. 1,5,3,6,2,4.

 

[achris]

Re: manifold filling with gas/low compression

Thanks bondo - Your right I forgot to open the throttle on the compression test.

Bond-o??????


.

 

[ziggy]

Re: manifold filling with gas/low compression

points at 16*

that's correct if ya mean .016", dwell @ 31*-34* would be best

fuel pump line into bucket good strong sguirts.

maybe them strong squirts are to much.....3-5 psi is spec...
ya didn't mention timing..... 6* btdc @ idle...

 

[starsnstripers]

Re: manifold filling with gas/low compression

Yep! aware of 6* BTC I dont have a fuel pressure gauge so uh ha thats a guess. it's getting gas to carb though. What would make a mechanical fuel pump have to much pressure? I figured they just got weaker and less pressure?

 

[achris]

Re: manifold filling with gas/low compression

DANGER WILL ROBINSON, DANGER

I think we have all been assuming this is a Mercruiser BUT!!!! look what I found..... Little wonder he changed his screenname

http://forums.iboats.com/showthread.php?t=230923

It's an OMC!!! Run away!!!!

Chris.....

 

[starsnstripers]

Re: manifold filling with gas/low compression

AAAHHH! Are we "lost in space" let me help! Chris that is a boat i'm going to be getting yes were talking about a Mercruiser 250 165hp! Earth to Chris "come in" OK behave Dons gonna beam us outta here at warp speed ! hat hum ! What makes a mechanical fuel pump pump to high of pressure?

 

[achris]

Re: manifold filling with gas/low compression

I think I've got snow-blindness. Is that the mountain calling??? Gotta go!!!

The only thing that would cause a mechanical pump to produce too high pressure is the spring above the diaphram being out of spec, but they would normal go low not high. What pressure are you getting?

Chris.....

 

[wncrjb]

Re: manifold filling with gas/low compression

Back to the low compression for a second.......
IF all cylinders have consistently low compression on a used motor, couldn't that also be a sign of an extremely wore timing chain, allowing the cam timing to be retarded a few degrees?

wncrjb

 

[starsnstripers]

Re: manifold filling with gas/low compression

Dont have a fuel pressure gauge Chris i just checked it pumping into a bucket and it looked good/normal. And this engine was a rebuild with low hours out of a lobster boat but it sat on it's side in the bottom of the boat and got a little weathered !

 

[Lakester]

Re: manifold filling with gas/low compression

hello,

sounds good on dist. compression stroke,TDC, set timing BTDC per book and rotor at #1. but...

do urself a favor if u havent...

and with the dist loose, and the ign ON... rotate the dist until u get the plug to fire. have it so u can see it fire. so rotate back and forth... so as that it fires consistantly every time. then dial it in so just smidge rotation fires it. this will have ur timing within 1-3 degrees of actual when u out timing light on it. u sed this with -0- advance...

yes, the dwell reading would be best. but hard to do a dwell reading if the engine isnt running... much less running as it should be. .016 should be OK to fire coil. if in doubt err on the tight side. set them .014 - .016. then tweak in or out at points when running smooth.

if it was mine, i would not be running it hit or miss... as it is hard on the cam and its lobes and lifter bottoms. engine must be set up to squirt gas, hit ignition and crank, and it comes to life and idles, then raise rpm to 2000 if new lifters. 650-750 if same lifters went back in same hole. if one new lifter it has to be honed in... 2000 rpms.

go back and set up ur ignition as mentioned here. get it spot on.

then be sure u have steady stable pump shot at carb.

if valves set and all else in place...let 'er rip!!

shoot a vidcam and post it to uTube and link it here so we all can go watch it run...

regards

lakester

 

[starsnstripers]

Re: manifold filling with gas/low compression

Thanks lakester i will do all that when i get some parts and rebuild the carb. and we'll go for it again!

 

[Lakester]

Re: manifold filling with gas/low compression

Thanks bondo - Your right I forgot to open the throttle on the compression test. It's a 4 pt. engine stand, stable enough.

sns~u r a brave man! stable enuff ain't enuff for me!!! not for an L6!!


Specs on this gm 250 165 hp say compession should be 140 psi. and I have had the dist. out because I manually primed the system with the oil pump because I had a slack lifter which is ok now. With valve cover off set mark on tdc just before the intake starts to open. points at 16* plugs .035 fuel pump line into bucket good strong sguirts. I'm going to try a few things and start over here. New exhaust gasket rebuild carb new plugs they came with the motor anyway. Level engine stand. I will follow up with you guys on my progress. Thanks for all the pointers and suggestions. very appreciated! p.s. great responses

--------------
sns sez"

"With valve cover off set mark on tdc just before the intake starts to open."

NOPE, sorry! wrong as u have it stated here: that TDC is 180 out of phase! why do u want the spark plug to fire just before the intake starts to open... ????????


u want the TDC where compression is building. that is where u want the plug to fire. and both valves will be closed! u want to initiate ignition to allow flame front probagation to take place sufficiently so that combustion chamber pressures on the piston's crown maximize at the point the rod's arm = maxim leverage potential to the crank! that is why u set timing at BTDC point on crank. so u can get piston pressure to build. therein lies torque.

so if u r in fact 180 out, as u have stated... pull all plugs. use a remote starter switch or build one. dont do it on the starter. if u need to build got auto parts store get push botton starter switch, some 14 guage wire and 2 clips. hook it up to solenoid S and bat +. now thru switch u r hot to starter. now u can click, click click the engine over... a tweak at a time. then with remote connected and ur tie not in water pump pulleys... lol, put ur finger on hole #1. now click click the remote until #1 comes up on compression. if u miss it first time, nbd. just try it again til u get into the groove. then tweak it making compression, [warm pressure will blast out of hole indicating u are on compression stroke] get it to 6 BTDC or what ever the spec is. this is where ur mechanical side of ur engine needs to be.

u may only be able to get it close. the starter is powerfull with no plugs in. be sure they 'are' out! so note direction harmonic balancer turns. stop short of 6 BTDC. and somehow, screwdrive, bar or? turn engine further by hand to 6BTDC. i have put bolts into harmonic balancer or unloosened pulley belts, backed out bolts to lower crank pulley, used bar inserted between the 3 and then turned crank over by hand. but do it in its natural direction. if u miss and go over, then back down a bit and then crank it up to 6 BTDC.

she'll never run if ur 180 out of timing phase....

now then... follow my advice and go set the distributor as i am suggesting. if u have fuel into intake and all else is as it should be... expect it to run.

"we r rootn' for ya!!"

let us know

regards

lakester

 

[Robj]

Re: manifold filling with gas/low compression

Forget about the pump putting out too much pressure. It flooded probably because the float in the carb was not shutting off the fuel supply and it just kept pumping fuel, flooding and into the cylinders the fuel went. Rebuild your carb, make sure your float and needle are OK and that should solve your flooding problem. Follow Lakester's advice and check/adjust your timing, and make sure it is firing on the compression stroke.

Good luck and have a great day,

Rob.

 

[achris]

Re: manifold filling with gas/low compression

When you did the compression test, did you have the throttle open? If you didn't, .....

If you have had the distributor removed, then check that you don't have the timing 180 degrees out. Check that even if the dissy hasn't been out. And check the firing order too.

Chris.................

So why is Bond-o getting the credit for these suggestions?

Chris........... (niffed!!)

 

[Flukinicehole]

Re: manifold filling with gas/low compression

AAAHHH! Are we "lost in space" let me help! Chris that is a boat i'm going to be getting yes were talking about a Mercruiser 250 165hp! Earth to Chris "come in" OK behave Dons gonna beam us outta here at warp speed ! hat hum ! What makes a mechanical fuel pump pump to high of pressure?

Some fuel pumps have a spacer between them and the block to limit the throw of the pump arm. If this spacer is left out you will have more throw and have higher fuel pressure. I saw this happen on a 4cyl. my brother had. He had a bad pump replaced it and forgot to put the spacer back in. The engine was flooding out real bad so he gave me the carb. I went through it and found nothing he put it back on and had the same problem. I told him to check his fuel pressure and it maxed out the gauge (15lb. gauge). Put a spacer (5/16) and that was it fuel pressure back to 6lbs. So if you take a fuel pump and extend the throw you will get higher pressure.

 

[starsnstripers]

Re: manifold filling with gas/low compression

Sorry, Chris I see now you did mention that thankyou too ! lol As for the timing it is set on tdc at compression. I Think Your right Lakester I'ts been awhile since I've played mechanic. Thats basic intake,compression,power and exhaust. I'm going to triple check that and do it your way. took myself for granted and overconfident maybe. As for the carb i had the top off and the float and needle worked fine. Float wasn't heavy and shut fuel off. Foat adjustment was ok. But when pumping the throttle i never could see the accelerator spraying fuel in the throat. I'm gonna rebuild it anyway rubber prob. dry. thanks again, i'll update my progress.

 

[Lakester]

Re: manifold filling with gas/low compression

sns~

good luck to u...

say?... can u take a pix of ur setup on the engine stand and post it here ? no doubt some would be interested in seeing how u have rigged it up perhaps.

regards,

lakester

 

[Lakester]

Re: manifold filling with gas/low compression

So if you take a fuel pump and extend the throw you will get higher pressure.

and no doubt... an excessive amount of volume, as well.

regards,
lakester

 

[starsnstripers]

Re: manifold filling with gas/low compression

OK ok! I feel like an _ ss. I had the timing out 180* Thanks for picking up on that Lakster. I had it firing just before the intake stroke. DAH! :redface: Oh well, I'll still rebuild the carb and get plugs and exhaust gasket change oil and filter again. Prob. has gas in it from my stupidity. Don't know when i'll get back to it maybe by tue. I'll let everyone know how it goes and get a pick of the eng. stand. Happy New Year!