PDA

View Full Version : carb issue?


ggrimes13
05-20-2013, 01:58 PM
I think I have a carb issue but not sure. 1987 Tristar, 351 rebuilt with GT40 heads (before I bought it last August - I since verified the 3 ribs in head casting after learning that here in TT). Also "new" rebuilt Holley 4160 (part 80319 - by an aftermarket rebuilder). 50 hours on the overhaul. Motor would start only by pumping throttle, then would not idle below 1300 rpm cold. Once completely warmed up, it would idle in neutral and run OK except for some hesitation on acceleration.

While out for the off season, here's what I did: replaced points/condenser/coil with Pertronix Ignitor III & Flamethrower coil, set timing, replaced plugs with Autolite 764 (per info found in TT for GT40 heads). Then while waiting for spring to arrive, took time to go through the carb to check all settings. I couldn't find a spec for float height (sheet with rebuild kit 703-47 did not have it), so I set them parallel to bowl, installed the carb and cranked to fill bowls, then used the secondary bowl sight plug hole to check and adjust that side, then set the primary (which does not have the hole) the same.

Now it rarely idles at all, usually dies when going below 1200 RPM even after completely warming up. It did idle two times, allowing me to take it out for a test run (I live on a lake), and it acted the same as last year in regards to hesitation on acceleration. Working on the idle issue, I've tried adjusting the idle mixture screws both ways without success. Yesterday it wouldn't idle at all. Any advice on where to go next with the troubleshooting?

ggrimes13
05-20-2013, 08:00 PM
I'll add a little more info, still looking for suggestions. I changed all fuel filters. End of last season I added Seafoam then topped off the gas tank. Dist cap and plug wires were replaced by PO at the overhaul so I did not replace.

thatsmrmastercraft
05-20-2013, 08:17 PM
You might be dealing with a base gasket vacuum leak causing a lean condition. You may have some debris in the system that is not allowing the needle and seat to close completely when they need to producing a too rich condition. Are you seeing any black smoke or any soot build-up on your transom? Might take a look at a spark plug or two to see if they are black indicating too rich.

Post a pic or two of your carb as I suspect you may have an automotive carb on your boat. There are some marine Holleys with fuel bowl plugs but they didn't come on a MC.

Cloaked
05-20-2013, 08:24 PM
http://www.mastercraft.com/teamtalk/showthread.php?t=54417

.

ggrimes13
05-20-2013, 10:00 PM
Thanks for the feedback MrMC. I'll try to get some pics of the carb Tuesday after work, and pull plugs to check condition. And thanks also Cloaked for the link to a similar issue. My carb was incredibly clean having only 50 hours on it, but there's something wrong somewhere so I'll watch this thread for his results.

ggrimes13
05-22-2013, 10:39 PM
Pic of the carb installed by PO:
95437
Peeled off the sticker:
95438
After seeing this, decided I wasn't in the mood to spend countless hours tracking down what might be wrong with this carb. Better for me to start over with a NEW carb from Holley. Found a dealer not far away and order for 1-day delivery. Received this carb today:
95439
Installed, fired up, and runs great! Minor adjustments to idle mixture screws and RPM, took her out on the lake and seems all is well...I couldn't be happier!:) Now I can enjoy the long weekend instead of working on this...:toast: Thanks for the advice, in some ways I feel like I took the easy way out, when I was a younger man I wouldn't have caved in so easily. But at the age of 53, I just want to have fun with my kids and grandkids, not spend all weekend trying to get the boat running.:dance:

j.mccreight@hotmail.com
05-22-2013, 10:42 PM
Glad you got it fixed, I have heard terrible things about national carburetor...

Lumbergh
05-22-2013, 11:21 PM
http://i470.photobucket.com/albums/rr66/Lumbergh556/happy-endings.gif (http://s470.photobucket.com/user/Lumbergh556/media/happy-endings.gif.html)

Nice!

thatsmrmastercraft
05-23-2013, 01:00 AM
Good to hear that you are back in business.

ggrimes13
05-23-2013, 05:55 AM
a couple more pics for those interested. the rebuild from National Carburetor had a sight plug hole on the secondary bowl, and the choke vent was closed off with epoxy:
95451
The new Holley as no sight plug (per your comment mrMC) and a proper screen on the choke vent:
95452
Now that I've taken the time to read the FAQ on how to post pics, I find it rather fun to participate. I'll share some of the other things I've done on the appropriate thread. Thanks again for the advice and happy boating to all!:D

thatsmrmastercraft
05-23-2013, 08:41 AM
a couple more pics for those interested. the rebuild from National Carburetor had a sight plug hole on the secondary bowl, and the choke vent was closed off with epoxy:
95451
The new Holley as no sight plug (per your comment mrMC) and a proper screen on the choke vent:
95452
Now that I've taken the time to read the FAQ on how to post pics, I find it rather fun to participate. I'll share some of the other things I've done on the appropriate thread. Thanks again for the advice and happy boating to all!:D

Great job on the pics. We are always happy to have another active member with the capability to post.

It is interesting that the National carb comes with a sight plug. I suppose allowing customers to dial in the float level saves on returned carbs that won't work due to the float being set too high.

ggrimes13
05-22-2014, 09:30 AM
I’m reviving this thread since I’m surprisingly having issues with my NEW carb installed last May (prior posts above). At the close of last season here in Michigan, it started stumbling when accelerating from idle. Since it did not magically fix itself during the winter and is getting worse, I am now attempting to troubleshoot. First check was the idle mixture screws, and I found it will still idle with them turned all the way in (actually a little smoother that way). Any suggestions on a troubleshooting path?

thatsmrmastercraft
05-22-2014, 10:06 AM
You either have a vacuum leak at the base gasket or hose going to the PCV valve, or your power valve is ruptured. Could be a float set wrong. Spray carb cleaner around the base of the carb and see if the engine speed increases. Also take a look down the throat of the carb while it's idling and see if there is fuel pouring out. Also check to see if there fuel is flowing after you shut it off.

ggrimes13
05-22-2014, 10:30 AM
Thanks, I'll do these things tonight or in the morning and reply with an update.

ggrimes13
05-27-2014, 01:19 PM
Got delayed by the holiday festivities; back on this today. No evidence of vacuum leak around carb base or PCV hose using the carb cleaner method. Pulling 13-14 vacuum at the PCV port on carb base at idle (in another thread I saw this should be 16 - is this a problem?).
111811
Cannot see any fuel spray or drops while running at idle or when shut down, but there are some droplets on top of the throttle plates, looks like moisture condensation?
111812
I did not check any carb settings before installing this new Holley, and performance was flawless for ~20 hours or so. Today it still idles best with mixture screws all the way in. Should I go ahead and get the power valve out? If so, what's the best way to check it, or should I just replace?

drschemel
05-27-2014, 02:21 PM
I think I would be leary of anyone calling themself "King of Carburetors"!!

ggrimes13
05-27-2014, 02:25 PM
Yeah, that one is sitting on the shelf in my garage...

cruiser
05-27-2014, 03:58 PM
If you turn the screws all the way in it should stall. Check power valve. grab one end. if it spins it is bad. Replace

zekedog
05-27-2014, 08:12 PM
I fell for that National Carb "banana in the tailpipe" trick once. Then bought the real deal.

thatsmrmastercraft
05-27-2014, 08:44 PM
I reading through this thread again. If the new carb worked flawlessly for 20 hours, then starts to have problems, I would bet there is some crap in the carb. I would be inclined to take off the primary fuel bowl and see how things look in there. I would also look at accelerator pump function.

ggrimes13
05-28-2014, 04:21 PM
OK, next step is pull the primary bowl and have a look around. Stay tuned...

thatsmrmastercraft
05-28-2014, 04:23 PM
:popcorn::popcorn::popcorn:

ggrimes13
05-28-2014, 08:08 PM
Pulled the primary bowl and metering block, found no evidence of dirt, gunk, debris...nothing.
111951
111950
111949
Went ahead and disassembled needle valve, no dirt there either. Blew compressed air thru all passages. Noticed the power valve is 2.5 and from what I've read it should be 1/2 of the vacuum at idle, so should be 6.5? However, doesn't seem like that would help my symptoms anyhow. Kinda feel like I'm back at square one. The pictures make it look like the power valve stem is off center but it's just the perspective of the camera angle. It looks fine, no obvious issues. Should I replace power valve while I have it open, and with what number? Anything else I should check?
111948

thatsmrmastercraft
05-28-2014, 08:11 PM
That is the correct power valve. It does look plenty clean.

Cloaked
05-28-2014, 08:12 PM
http://holley.com/data/TechService/Technical/power_valves.pdf

Also........... I think you used internet pictures. That carb is too clean..... :D

.

thatsmrmastercraft
05-28-2014, 08:12 PM
Tip that fuel bowl so the float is upside down and ensure that the float is level.

ggrimes13
05-28-2014, 08:33 PM
I wondered about that...it's not "level"
111960

Cloaked
05-28-2014, 08:40 PM
I hope you get this resolved, truly I do..... nothing more frustrating... but have patience...

Best on resolution....

ggrimes13
05-28-2014, 08:45 PM
@Cloaked: The National carb was on the boat when I bought it, but I replaced with a new Holley last year (that's why it's so clean!). Started having new issues at the end of the season. Now troubleshooting the Holley...

Cloaked
05-28-2014, 08:48 PM
@Cloaked: The National carb was on the boat when I bought it, but I replaced with a new Holley last year (that's why it's so clean!). Started having new issues at the end of the season. Now troubleshooting the Holley...
yes Sir, I went back and read that in between the pictures, thus the edit....

I still say your carb is too clean... :D :D

.

ggrimes13
06-01-2014, 08:33 AM
So...after reading countless tips on various forums dealing with unresponsive idle mixture screws on Holley, I decided to try adjusting the stop screw of the secondary throttle. From what I read, this might help if the primary throttle is set too far open to get correct idle speed, exposing too much of the idle transfer slot.

I put the primary bowl back on with no changes, and made a special slotted 'screwdriver" out of a spare allen wrench to be able to turn the secondary stop screw without removing carb. Sure enough, this raised idle speed so I could back off the idle set screw and then mixture screws were responsive. Still not as much as I expected (engine does not die with them bottomed out) but definitely idles smoothest and pulls highest vacuum with them 3/4 turn out.

I tried going further with the secondary but then it raised idle speed so far that I ran out of adjustment to lower it with the idle set screw. I ended up with the secondary stop screw 1/2 turn further in than it was. I can't say how many turns from first contact since I didn't check that setting before installing this new carb, and it was too much of a pain to turn that screw back out to verify (tight spot, hot motor, etc..). If I ever take the carb off, I'll check and record that setting for future reference.

Lake test appears successful, no more hesitation or backfire:) Internet pic below just for reference showing the secondary adjustment screw in base of carb.

112177

ggrimes13
07-15-2014, 11:40 PM
After all the fiddling I have done to my new Holley 4160 I still ended up with occasional hesitation and backfire, which continued to get worse. Long story short, I went back thru the basics and upon close inspection found an internal crack in distributor cap extending between two posts :o. Replaced cap and so far seems to have fixed the problem. Lesson learned...don't assume anything. I didn't see any issue with the cap when I converted to Pertronix last year, but now kicking myself for not replacing it at that time. Hope this helps someone else chasing similar problems.:)