1984 228 305 carb problem

[FORREST3]

Hey all.. boat/engine is a 1984 chaparral 196 XLT, I/O 228 305 merc. original 4 bl. qJET Merc # 1347-8296A4.. carb# 17080565. Out of water results BTW..Engine rebuilt 2 years ago.. ran fine ..now finding plugs are showing rich.. inspected primary venturies , they are dripping fuel at idle/ neutral.. rpm is 900..lower the idle to 6-7 hundred ( no load,out of water) stops dripping. . I installed throttle shaft bushings in prim. and sec. a year ago or so.., ( not that that matters with this problem). Bought a carb kit yesterday.. replaced needle/seat gaskets etc.. fuel pressure at 6.4 or so..Vac. at idle is at or right above 15 inches... power piston spring unchanged..(same spring).. idle mixture screws barely/not responsive.. timing correct ( 8 degrees btdc)..float level set at 1/4.. bowl plugs pressure checked o/k.. idles/neutral around 900.. runs fine.. but rich at idle..getting too much fuel at idle.. disconnect a vacuum source ( rear engine unused nipple), idle goes up, and I'm stumped?..only thing I can think of is p. booster spring too strong now? :LOL..What else could be causing this? So under load if I put in water, (in water in gear rpm's down to 550-600 maybe no leaking?) Own a shop restoring classic muscle cars so I'm pretty good with Q JETS..I realize I may be pushing the envelope here but maybe someone had the same issue! Not called Cliff Ruggles yet! Might get lucky here first! I hate it when I'm stumped!.. Thanx for any suggestions.. Forrest

 

[Scott06]

You’ve checked most of the low hanging fruit I’m thinking your fuel pressure is a tad to high ? Is float water logged ? If you turn idle speed down thinking fuel pump being slower outs out less pressure ?

Had the same thing in my gto this morning lowered the fuel pressure regulator half a turn and stopped dumping fuel down front carb at idle …

 

[FORREST3]

Thanx! That's hilarious!.. I specialize in restoring to #1 levels 69 -72 GTO's!..Been restoring them for 26 years.. LOL.. anyway.. not sure if 6.4 fuel pressure is too high,not sure what is correct? Newer correct fuel pump installed also a while ago, Float is fine..I'll try regulating pressure lower..this fuel rich problem may have been going on for quite a while without noticing till now. Any other opinions? Thanx! I really appreciate it

 

[Bondo]

Thanx! That's hilarious!.. I specialize in restoring to #1 levels 69 -72 GTO's!..Been restoring them for 26 years.. LOL.. anyway.. not sure if 6.4 fuel pressure is too high,not sure what is correct? Newer correct fuel pump installed also a while ago, Float is fine..I'll try regulating pressure lower..this fuel rich problem may have been going on for quite a while without noticing till now. Any other opinions? Thanx! I really appreciate it

Ayuh,..... 6 psi is the upper limit on carbs,....

 

[FORREST3]

Thanx Bondo// and scott...the q jet carbs I usually work on for early Pontiac GTO's..(400 or 455 cid.) could run at around 6.2 psi..So I assumed this carb MAY be o/k with that?..So my next move will be to regulate it down to 5.5? I will let ya'all know!..Thanx! Forrest

 

[Scott06]

Thanx! That's hilarious!.. I specialize in restoring to #1 levels 69 -72 GTO's!..Been restoring them for 26 years.. LOL.. anyway.. not sure if 6.4 fuel pressure is too high,not sure what is correct? Newer correct fuel pump installed also a while ago, Float is fine..I'll try regulating pressure lower..this fuel rich problem may have been going on for quite a while without noticing till now. Any other opinions? Thanx! I really appreciate it

Mine is a 65, the tripower can only handle about 3.5 psi. i found when i replaced my fuel pump the new one put out way too much pressure.
if you are weeping of the venturis at idle its either fuel pressure too high or float/ needle and seat.

might be worth post on cliffs q jet forum what fuel pressure will work. Im sure youd get a definitive answer.

does your GTO shop have a web page ? Pm me it would like to check it out.

 

[dubs283]

900 idle speed is too high. 6-700 is appropriate for an mcm engine. Best to check/set idle in gear on the water.

Idle air mixture will not respond much if at all at 900 rpm because at that point the idle circuit is bypased by air pressure drawing fuel through the venturis. Should see steady vacuum of 17 on a sound engine with proper ignition/carburetor tune

 

[Scott06]

900 idle speed is too high. 6-700 is appropriate for an mcm engine. Best to check/set idle in gear on the water.

Idle air mixture will not respond much if at all at 900 rpm because at that point the idle circuit is bypased by air pressure drawing fuel through the venturis. Should see steady vacuum of 17 on a sound engine with proper ignition/carburetor tune

Agree on the idle speed, but at 900 rpm the carb will still be on the idle and transition circuit. on a properly set up carb you wont see fuel coming of main venturi until 1800-2000 rpm give or take… you can see this if you look straight down the bores and slowly open the throttle. Fuel flow of venturi is clearly visible, but it is surprising how long the carb runs off the idle and transition circuit before mains take over. There isnt enough vacuum signal at low rpm to pull fuel

 

[dubs283]

on a properly set up carb you wont see fuel coming of main venturi until 1800-2000 rpm give or take…

Not true.

Transition circuit does come into play at just off idle, with relief from the idle circuit. But once the throttle plate opens long before rpm reaches the speed you mention the 14.7 psi air pressure (atmosphere) overcomes the idle circuit (located below the plates, i.e. vacuum) and venturis release fuel.

OP needs to lower idle speed and quit thinking about cars when working on a boat

 

[Scott06]

Not true.

Very true.

video your carb...at 900 rpm if properly set up no fuel will be coming out of the venturis

 

[dubs283]

Don't own a carburetor, just work on them

And understand how they work on marine engines

 

[FORREST3]

900 idle speed is too high. 6-700 is appropriate for an mcm engine. Best to check/set idle in gear on the water.

Idle air mixture will not respond much if at all at 900 rpm because at that point the idle circuit is bypased by air pressure drawing fuel through the venturis. Should see steady vacuum of 17 on a sound engine with proper ignition/carburetor tune

Thanx..All work is OUT of water with muffs.. The mercruiser manual says 650-700 IN GEAR (under prop load).. so I assume (out of water) 900 rpm or a little less or so OUT of gear out of water no load is close? Scenario in or out of water in neutral should be the same.. Correct?( venturies dribble).set fuel pressure to 5. Vac. is right 15.5 at 800 rpm's (same as two of my 400 455 c.i.d. 1970 GTO's at idle (Q-jet's).. at 800 rpm at idle..If I drop the idle anymore on boat, vac. falls below 15 and runs a little rough..still dripping at 600-750 rpm's..The only thing I can think of is the p. piston spring being too strong? Even tried advancing the timing for kicks..No difference..LOL.. Whats left? Rebuilt dozens of Q-jets. THIS is (hours &hours!) very frustrating.. Really appreciate it! Maybe I'll cut a few coils off the p. piston spring..What else to do..Thanx

 

[FORREST3]

Dubs283 said .."OP needs to lower idle speed and quit thinking about cars when working on a boat".. I get it! That's why I'm at your mercy.. Just to be clear.. What's the difference if running on muffs, next to my shop and engine/outdrive in "idle/neutral" and if boat is IN the lake and engine/outdrive is in idle/neutral..am I missing something? So is being on the lake and engine/outdrive in neutral/idle going to change this dribbling in neutral/idle like it's doing next to my shop..LOL? Thanx again..

 

[dubs283]

You can set the idle to whatever speed you like. Spec calls for 6-700 in gear. That means in the water, in gear. You need a load on the system for you to adjust properly.

Boat is intended to work properly in the water. Can't see too many people sitting in their boat on the trailer loving life

Vacuum should increase with lower rpm. Are you sure the engine mechanical is sound?

 

[FORREST3]

Thanx Dub... but...dubs said.."Vacuum should increase with lower rpm". My Vac. source is from top of intake manifold..every Qjet I have/had is higher the rpms the higher the vac. lower rpms IS lower vac..Now ported vac. is the opposite ( used for distr. adv.. etc..). Compression all cyl. is 125-130 psi..pushes the 20 foot fully loaded bow-rider Chaparral to 50+ mph..all is good but the fuel rich issue.. I appreciate it!..Lookin for some p. piston springs here..don't know what else to do..should not drip fuel at 700 in neutral idle, in or out of water..Also rpm's should NOT jump up a few hundred when opening a vac. source on the intake at idle.. It's been running rich for a while, (black sp. plug tips, and other things) I just noticed this now because was doing a tune-up. and stumbled into a "darker" issue...Thanx..

 

[dubs283]

..should not drip fuel at 700 in neutral idle

What happened to 900 rpm idle speed?

rpm's should NOT jump up a few hundred when opening a vac.

You do not understand how a naturally aspirated gasoline internal combustion engine works

 

[Rick Stephens]

Just to be clear.. What's the difference if running on muffs, next to my shop and engine/outdrive in "idle/neutral" and if boat is IN the lake and engine/outdrive is in idle/neutral..am I missing something? So is being on the lake and engine/outdrive in neutral/idle going to change this dribbling in neutral/idle like it's doing next to my shop..LOL? Thanx again..

Don't know if being IN the lake will change the dribbling or not, but the back pressure on the exhaust from pushing it out a foot under water does change your mixture as exhaust evacuation is under pressure.

 

[FORREST3]

I lowered the idle, good grief...I know VERY well how NA engines operates...Properly running early v8 Qjet engine should not jump up hundreds of rpm's with a huge vac. leak and run smoothly....I have a complete restoration shop..with just about every tool imaginable.. been rebuilding classic muscle cars for 26 years.. I do ALL the work ( body,interior, engine with exception with boring and valve jobs....Kinda insulted..What made you say that?.. Just curious..what exactly are you disagreeing with me about? I agree I'm NOT a boat expert.. But I am VERY knowledgeable of mechanics and everything associated with it..Q jets are NOT my specialty especially with marine types..give a guy a break!..GOD...66 years old and never has anyone said to me what you said.. actually just the opposite...incredible..and sad

 

[FORREST3]

Don't know if being IN the lake will change the dribbling or not, but the back pressure on the exhaust from pushing it out a foot under water does change your mixture as exhaust evacuation is under pressure.

I really appreciate this info!.Had not thought of that! .I agree..Problem is that the engine has been running too rich for a while and really noticed it just a week ago..therefore my inquisitions.. Thanx a bunch Forrest

 

[dubs283]

If you're confirming your earlier post of saying a vacuum leak does not increase rpm then yes, you really do not know how a naturally aspirated engine works.