replacement engine, carb issue

[brucew]

Hi,

 

I've got a 1994 Tige slalom that I had to replace the engine. I got a 350 mercruiser with an edelbrock carb. I mainly use the boat in the course and have perfect pass. The engine has a flat spot in it's throttle response. When the skier load increases, it appears that Perfect Pass is doing its job, increasing the the throttle. But the engine initially doesn't respond, Perfect pass keeps increasing the throttle and then the boat surges. The RPM drops about 50 and then jumps about about 100 RPM. Perfect Pass  normally would keep the throttle plus/minus about 10 -20 RPM.

 

I talked with Edelbrock and they suggested getting a metering kit to change the carb jets and stage springs.

 

So now my questions

 

Has anyone had to modify their carburater to get a more responsive engine?

 

Has anyone used a Edelbrock carb for a slalom boat? I'm more familiar with Holy.

 

Thanks,

Bruce    

[DW]

Yes, I have modified my carb.  That engine comes with a Weber carb which is the same as the Edelbrock or is the same as a Carter AFB.  The Weber carb actually has a three stage needle whereas the Edelbrock only a two stage.  My first suggestion would be to verify which unit you actually have, the Weber will probably be painted black and there is a small Weber logo on the carb itself.  One test I would run would be a secondary spring test, remove to see if that makes a difference, if so, the secondaries are trying to kick in right at the spot you are running (what speed/rpm are you running?).  Weber parts are first class, so if that is the unit I would suggest keeping it that way but you can substitute some of the parts.  Don't mix jets and metering kits as they go in sets and the combination determines the fuel curve.

I would suggest a rebuild, the carbs tend to collect debris that plugs up the filters and sitting creates some debris in the bowls.  Cleaning and a light refresh will cure many stumbling issues with the carb.  Make sure the accelerator pump is fresh and clean, the inlet filter is clean, the bowls are free of debris and any passages are clear.  The accelerator pump squirter probably wants to be on the maximum throw position (lever on top front  with multiple holes in it). 

I have modified my carb, but because I wanted too not had too.  I have changed the accelerator pump squirter (richer), lightened the secondary air valve weights, changed some of the venturi parts, smoothed out the flow passages, basically blueprinted the carb and optimized it for performance.  David Vizard has a good book as a reference on the Carter AFB carb with lots of good tips.

[Roger]

It sounds like the same problem we used to have with the spread bore carbs and PP. All we did was disconnect the secondaries.

[Jody_Seal]

Get rid of the AFB and replace with a Holley you will be happier for the replacement. The marine AFB and their clones are always in need of adjustment and the fiddle factor never seems to go away. If you want to adjust it and walk away then Holley! Want to play with it and like the challange well so be it stick with the AFB.

The AFB does work well on what they were designed for, Big cubic inch Mopar!!!

[DW]

My experince does not match Jody's experience, but mine is only a sample of size 3 different boats.

[RichardDoane]

I agree with Jody, put the AFB on Craigslist, install a Holley, and go skiing !

[Alberto Soares]

I had a boat with a Holley, it used to surge at 36mph just like yours. I disconeted the metal part that activates the second stage, it worked just fine after that...

[DW]

Bruce, attached is a Weber carb parts list and exploded view picture. 

As for surging from engaging the secondaries, you could change the prop pitch a bit to alter the engine speed and throttle position to move out of that range.  The engagement point of the secondaries can also be changed by adjusting the linkage on a mechanical version, engine speed will do it for vacuum actuated secondaries.  The common "fix" is to disconnect the secondaries as noted previously but then they won't open so top end performance will suffer.

[Roger]

Disconnecting the secondaries takes 30 seconds and costs nothing. I'd certainly try that first before buying a $650.00 Holley.

[Jody_Seal]

4160 Holley. $475.00 From Florida Inboards PCM Dealer. $499.00 from DIM same Carb specificaly formatted for ski boat , includes gaskets. , has blue cam and correct powervalve so secondary's will not come into play at 36 mph slalom.

Old AFB will sell on evil-pay for $75-$150 or more!

Where did you get the $650???

[Roger]

Sorry, haven't bought a Holly since the 70s, got the price from Overtons:

http://www.overtons.com/modperl/product/details.cgi?i=22245&pdesc=Holley_Marine_Carburetor_80552/4175&str=holley&merchID=4005

So my sentence should read:

Disconnecting the secondaries takes 30 seconds and costs nothing. I'd certainly try that first before buying a $475.00 Holley.

 

[Jody_Seal]

Yea disconect the secondary's on a four barrel intake and run a couple of cylinders lean!!!!! old waterskiers trick! Why not set the boat correctly? Then again As a engine dealer I would rather sell a replacement engine anyway over a carb.... 

[RichardDoane]

disconnected secondaries will lean out all the cylinders equally, left bank/right bank, if it has a split intake manifold

[Jody_Seal]

If you say so!! lets see engine mounted at 14* ! OK!! left bank, right bank??? front, rear???? Makes no difference to me being cheap only works for the short run anyway. Would rather see a engine properly setup and tuned correctly then shade tree ideas and old school thinking. At least if the carb is not going to be replaced tune it and put the correct parts in it for the application needed.  Or Fiddle Factor!!! /vanillaforum/js/tinymce/jscripts/tiny_mce/plugins/emotions/images/smiley-smile.gif

[brucew]

Thanks for all the comments.

The engine and carb are new, not rebuilt.  the carb is an edelbrock 1409 marine carb. From what I've seen, the problem 

isn't an overactive secondary but more of non-responsive carb. The RPM drops off about 50 RPM and PP is telling the engine to pick

up RPM. I've run the boat with the engine cover off, and PP is aggressively pulling the throttle forward. Eventually the engine responds,

but PP has been saying to pickup RPM and nothing has happened. Then, the engine finally responds 

and surges around 100 RPM. So you're getting a net of +/- 50 RPM which is way too much. My friend I ski with has a MPI 350 Mercruiser and the RPM 

variation is only about 10 RPM.   I've heard that the Holley has a primary and secondary accelerator pump but the Edelbrock only has a primary.

 

I've been able to reproduce the problem at 30, 32 and 34 MPH, so the problem doesn't appear to be isolated to a certain speed. Tomorrow I should be getting

my metering kit and will give it a try. The vendor I bought the engine from could have provided me with either a Edelbrock or Holley. Seems they didn't provide me

with the right configuration for a tournament ski boat.   

 

[kdeupser]

Bruce, it sounds more like an accelerator pump issue to me.  I'm running dual 625cfm carters on my Mustang.  I had to switch to carters from holley's due to the intake manifold.  I bought 4 junk carters at a swap meet, came home tore them apart and rebuilt two very nice carbs.  I've obviously purchased the Carter Trackpack that has many many different jet's and metering rods.  You should see my tuning spreadsheet!  Whew!  However, all the tuning has paid off nicely, she idle's very well at 1,000rpm(due to large cam) and pull's very strong into 6,500rpm.

Dis-connecting the secondaries on a holley certainly will not hurt anything.  I have a friend's boat that's a 93' Mastercraft Promo boat that has had it's secondaries dis-connected from almost day 1.  The boat has over 2400hrs on it and still running strong.  Now if you start changing your primary jet size that's a whole new matter, which I'd be glad to help you with offline.  Timing will come into play as well. 

For what it's worth, the powervalve on a holley does not have any thing to do with the secondaries coming in.  In fact you can buy different power valves that come in at different manifold vacuum pressures.  Same for the secondaries on the vacuum operated carbs.  You can buy a spring kit from holley to adjust what vacuum level you would like for them to come in.  We tried every spring in the kit on this 93' which has the latest version of StarGazer.  The secondaries made the boat evil to ski behind.

I'd recommend changing out your accelerator pump.  It's cheap, quick, and easy.  Here's a link for one. 

http://www.summitracing.com/parts/EDL-1470/

You can also adjust when the accelerator pump comes in on a carter.  You should have 3 or 4 holes in the level that connect's to the pump itself, by relocating the pump to each one of these holes brings the pump in at different rpm.

Jody, Richard, please don't take my post wrong.  You guy's know alot more than I do, I just have messed with carburetors for along time.

Carters are good carb's, you just have to be patient.  You can tune either the Carter or Holley down to your craziest wish if you have the time.

 

Good Luck,

Ken D.

[DW]

Bruce, your note brings up a couple of questions,  1.  do you have the wedge plate mounted on top of the intake manifold to level the carb?   2.  Is the accelerator pump (actuating arm on lf corner of carb) in the top hole (most aggressive)?   3.  do you have any air leaks, it sounds like that is a potential issue.

My boat has the Weber version of the carb and it is very responsive and there is no surging at all with a constant or even slightly changing throttle position.  Correct on the pump, only one.  You might look at the needle jet springs, accessed easily from the top of the carb, you can see them in the pdf I attached, item 4 listed as a metering rod kit but you can get the parts separately as Ken notes from Summitt.  Make sure you have or use the lightest springs available, that will richen the mixture earlier or quicker.  I read the anti Carter comments on this post, but quite honestly my particular boat is more responsive and just as smooth as any FI boat on the lake, although it is not stock but the fuel system is not a limiter.  The only real complaint I have is the bimetallic spring on the choke is not quite matched so I have to adjust the choke twice a year for the cold and warm seasons, but that is no big deal.

[brucew]

Okay, I checked the accelerator linkage and it's in the top hole which would make it more aggressive. Don't have the boat set up to run right now, but earlier I moved the throttle by hand while the engine was running and the pump output some gas. I'm getting a metering kit this afternoon and will start with putting in step stage springs. Edlebrock recommends using stiffer springs, pink or silver, to keep the rods up to make the fuel richer.

DW - you said lighter springs which I think we make the mixture leaner not richer.

 

The wedge is installed between the intake manifold and carb. New gaskets were placed on either side of the wedge. I don't see any leaks, the vacuum port is covered with a plastic fitting to seal it off.

 

[DW]

Bruce,  for the Edelbrock you are correct, a heavier spring will lift the needle sooner. 

[brucew]

Thanks DW

I got the metering kit and put in the silver stronger springs. Made sure the existing metering rods were correct. I didn't take off the air horn to check the metering jets.

Pulled a spark plug - looks just about perfect, maybe slightly lean but certainly not rich.

I'm thinking my problem isn't the secondary or the accelerator pump. PP is only trying to make slight adjustments, not a heavy throttle increase. So hopefully making things a bit richer will solve my problem.

Will be going to the lake to try things out this weekend.

 

 

 

[brucew]

Well, I finally got out to the lake to test the changes and I'm VERY DISAPPOINTED with Edelbrock carbs. I've had enough and will be switching to Holley.

I installed the stronger silver step up springs and they helped some. Still way to much hesitation and surging to use in the course. So I took out the metering kit and looked for 

a metering rod that would give me a richer mixture according to the Edelbrock tuning manual. That's when I found out that the metering kit only includes about 1/2 of the metering rods/

jets combinations mentioned in the manual. It's easy to change out the metering rods, more effort to pull the air horn to replace the jets. Especially when the boat is rocking in the water 

and the sun is rapidly setting. So I took off all 8 tork screws to remove the air horn. Tapped it a few times to get it lose but it was still stuck. Tapped a straight blade screwdriver in the crack

between the carb body and air horn and pryed up to seperate the two. Got them slightly apart but I felt if I pryed any harder, I could break the air horn. So I gave up.

This is new engine with a new carb that I bought from Michigan Motorz. I told them it was for a ski boat and the gave me a setup that is non functional.  I've lost over a month of the ski season

messing with this. I can understand tuning a carb to get maximum performance but it should not be necessary to get adequate perormance.

 I will talking with Michigan Motorz tomorrow to see how they plan to correct this problem

I'm extremely frustrated with the situation. 

Bruce

 

 

[DW]

Bruce,

Sorry to hear things did not go well.  There are actually 9 screws to remove, I have attached an Edelbrock diagram, see item 16 & 17 on the breakdown.  It sounds a lot like an air leak, your description of the characteristics would suggest that, add fuel and it runs better along with a surging problem.  I assume you have checked to make sure a Marine calibration is in the carb, they are a bit different than a standard vehicle calibration.  Edelbrock should have a spec sheet to help you on that.  I would certainly be checking for an air leak, a spray can of starting fluid or brake clean can help you isolate the location of the leak.

[Jody_Seal]

Now thats funny!! Sorry !/vanillaforum/js/tinymce/jscripts/tiny_mce/plugins/emotions/images/smiley-laughing.gif

Fiddle factor!! Good Idea get a Holley you will be much happier. Make sure you get a new one and not someones re-done POS! Hell I will not re-build any carb  for customers because I can sell new for a few dollars more and warranty it. PCM Part number RAO52003. These carbs are pre calibrated for waterski usage. I like to put a Blue Secondary cam on them and forget it, However if you just want to install and go they will do just fine from the box. Florida Inboards price $469.00. DIM Price $499. Who ever you buy from make sure you either have a steel feed line or a aeroquip braided line DO NOT USE FUEL LINE FROM FEED PUMP TO CARB!

Good luck!

[DW]

Bruce,

Have you confirmed that the boat has the same characteristic when not using PP?

Has Michigan Motorz ever supplied a ski boat setup before?  That would be a good question for them, and if not, what criteria did they use to set it up?  A carb is not a "smart" item, it simply mixes an amount of fuel depending on how much air is passing by the venturi or more specifically, by how much air pressure depression is in the venturi.  Add a little extra for fast throttle openings (accelerator pump) and there you go.

[brucew]

agh!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I spent the last couple of hours going back and forth to create a detail post and then when I went add your comment, I had timed out and the post was then erased by the login screen.

 

So this is a much condensed version.

I found the 9th bolt. It's the long bronze bolt that the air filter on It intially looked like it just went into the air horn, not the carb body. The manual only says to remove 8 tork bolts. 

I'm going to install option #18 in the tuning manual, page 26 which is 3 stages richer on power and 2 on cruise.

I've looked into Holley carbs. Probably want 4150 which has a manual secondary, not 4160 which has a vacuum secondary. Calling around if they also do special jetting from this for a ski boat. 

Going to the lake now for another test, will update later.

Thanks for the continued help. 

 

 

 

[brucew]

Okay, it's much better now. Total RPM movement is around 20 RPM from load to noload. Engine is noticeable more responsive. I made it 2 stages richer in cruise and 3 stages richer in power mode per the Edlebrock tuning manual.

I've only been able to simulate a skier load by doing a slight turn and then straightening out. Earlier this technique had been able to reproduce the same problem I saw in the course. Now I don't have the problem.

Idle is a bit rough, so it's probably too rich. Going to the course this Friday and will update again with results. 

I didn't do the test for air leaks - not that comfortable spraying starter fluid on a hot engine even with a fire extinguisher handy. 

 

[RichardDoane]

A safer way to check for vacuum leaks is with an unlit propane torch, just crack open the valve and point the nozzle along the seams/areas you want to check. Years ago, while checking a rotten old Jeep Cherokee for vacuum leaks with carb cleaner, I had the entire engine become a ball of fire (with my customer watching). Luckily, no serious damage occurred to the vehicle, just to my pride.

[DW]

I have always done it with the engine just fired up and cold, not fully warmed up and hot.  Propane torch is a better alternative.  Soounds like that is not an issue based on latest feedback.

[brucew]

Okay, back from the course and everything worked well. I will need to monitor to see if I'm running richer then I need.

Then it's back to fiddling. Idle was okay today. Really bothered me that I needed to do this with a new engine. Out of the

box, the Edelbrock carb had a flat spot that no one would want, even in a big powerboat that you're just  cruising with.

If I had my choice, I'd probably go with the Holley 4160 for a ski boat. A great source of information is Florida Inboard Marine.

They really understand marine performance carbs. 

 

[DW]

What was the cure for the flat spot, different metering rods?  It unfortunate, but there is expertise behind tuning for marine vs. street usage.  Glad there was some help out there to solve your problem.

[brucew]

The tuning manual is in the boat down at the course lake, so this will be from memory.. I ended up switching to a richer jet and richer metering rods as well as going to the strongest step up springs. Probably richer by 2X or 3X. I'm probably richer then I need to be. I'm a lot more interested in skiing then fiddling. The course lake I ski at is busy, so it's not the best place to fiddle. So I need to haul the boat to a public lake and pay an $18 launch fee to do my fiddling. I'm a better fiddler now, but my first couple of trys was a learning experience without a lot of results. In October, when my lake isn't as busy, I'll try to fine tune my fiddling.