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Index > Engine/Drivetrain > Thread: carb reccomendations
Thread: carb reccomendations
dman1049


Newbie
Posts: 9
posted March 08, 2011 08:19 PM

carb reccomendations

I have a dellorto carb on my 13b out of a rx7 in my REPU, problem is the low end its to much carb but up top its perfect. I need to know what to do to fix my carb problem of sputtering,coughing, backfiring, starting and idling problem. Can someone please shed some light on my problem.

       
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Brad


Rotorhead
Posts: 1672
posted March 08, 2011 08:32 PM

What is all of your jetting? Are the floats set right? Fuel pressure gauge just before the carb set at what pressure? Clean all the jets out with carb cleaner w/straw or better yet soak them in a carb dunk tank first.

Lots of good Dellorto info here. http://www.gruntled.com/Dellorto/

If you need it rebuilt, let me know. I can do it for you.

Sounds like floats are hung down, needle and seat stuck open due to dirt, or too much fuel pressure.
____________
-brad-
74 REPU Lawn Green
81 Rx-7 racecar. 12a J-
Bridge

       
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dman1049


Newbie
Posts: 9
posted March 08, 2011 10:25 PM

to be honest i dont know on jetting, the truck is a hand me down hand me down, my grand father bought it new in 75 my dads tinkered on it and now im having to drive it. Im 18 i have spent time around the rotary. its a 13b engine. This carb has always done this. I do know there isint a fuel pressure regulator, it does have an electric fuel pump tho. My father spent weeks tinkering with the carb and its not any better than its always been. I think its way to rich on the bottom, and air fuel mix is off. I dont know what screws on the carb do what. Under load the motor loads up, at idle it loads up, it sputters, coughs, dies , and backfires unless i drove it like i stole it. What is needed for me to find out so i can further help you help me out on fixing it so it runs right?

       
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Brad


Rotorhead
Posts: 1672
posted March 09, 2011 09:30 AM

There is a schematic on this web site: http://www.gruntled.com/Dellorto/ where you can see where all the jets are.

You should take the lid off the carb and set the floats and make sure they're not soaking up fuel.

Then remove the main and idle jets. They look like 4 brass screws. Look at the number markings and write them down.

We'd assume your running the 39mm chokes that came with the carb but you really should check that too. You have to look down the carb throats to see the # imprinted on them.

Also pull the accelerator pump jets and check the # on them.

Clean everything with carb cleaner or brake cleaner. Buy 2 cans and don't be shy with it. You really, really need to install a fuel pressure regulator and fuel pressure gauge. It sounds like too much fuel is getting into the carb so I'd bet pressure is too high, floats too low or soaking up fuel and dropping, or needle is not able to seat due to debris in the seat.

I read this book before I took anything apart. It is excellent.
http://www.amazon.com/Build-Power-Dellorto-Carburettors-Speedpro/dp/1903706750

       
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dman1049


Newbie
Posts: 9
posted March 09, 2011 10:42 AM

Where should i place the fuel pressure regulator? I was thinkikng about checking the floats. My father like i said went through the whole carb so cleanign it all i dont think wll get me anywhere. I will check floats and get a regulator. what should i set the floats to? As far as i know the only thing thats been replaced is the jets, but im not sure so ill have to pull them and look.

       
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gysgtfrank


Newbie
Posts: 5
posted March 14, 2011 04:23 PM

The Vintage Rotaries site has a pretty good post under carburetion for jetting on the Dellorto and Weber.
____________
1979 RX7 S Model
1975 yellow&black REPU-sold

       
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mattraver


Revvin Up
Posts: 95
posted March 14, 2011 10:25 PM

i keep my regulator in the engine bay ,as for the carb and manifold ......well they dont work well ,racing beat will tell you that fact . a holly is great for maximum HP but stutters when hanging a sharp corner.the webber is about 10 HP less across the board but great for corners and very simple to tune

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dman1049


Newbie
Posts: 9
posted March 14, 2011 10:27 PM

do you guys put the regulator before or after your fuel filter? what regulator do you recommended?

       
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mattraver


Revvin Up
Posts: 95
posted March 14, 2011 10:38 PM

tank ,filter,pump then regulator. holly reg is alright for the price .also fuel pumps need to be gravity fed or pump will wear out quick

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dman1049


Newbie
Posts: 9
posted March 14, 2011 11:37 PM

i have a filter right before the fuel line goes into the carb, i feel some corners have been cut by my grand father and father. i can here an electric pump kick on when i turn the key on, does this hurt or help me?

       
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gysgtfrank


Newbie
Posts: 5
posted March 14, 2011 11:46 PM

Another good site for general information on carb'ing a rotary is the Sterling Metal Works site. He's having some problems, so he's not building any carbs at the moment. His site though has some very good basic information, it's primarily geared toward the Nikki carburetor, but the basics are must know for pretty much any carburetor. As for filters, I always run one before the pump and one right before the carburetor usually downstream of the regulator. Although a case can be made for having a regulator just before the carburetor to ensure you are getting just the right pressure at the carburetor. If the pressure is off, it can cause symptoms like you're experiencing.
____________
1979 RX7 S Model
1975 yellow&black REPU-sold

       
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dman1049


Newbie
Posts: 9
posted March 14, 2011 11:58 PM

something else i noticed today was the oil pressure change, it usually reads between 40 to 60 psi, when i let it coast in neutral Ive seen it drop below 40 psi, is this bad or indicating a problem arising? I checked the oil and there was a milky foam on the top of the stick not in any of the oil on the stick, does this mean there is water in my oil? im not loosing any water, i know this because my radiator is full and my temp never gets about 190.

       
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mattraver


Revvin Up
Posts: 95
posted March 15, 2011 03:21 AM

you will hear the fuel pump ,thats normal .all after market pumps (holly ,malory ,etc) need to be gravity fed or the pump will not last long .my feed is the drain hole with a 90 degree hose fitting,something that is going to be changed in the near future to a weld in sump .the milky dipstick is normal ,there will also be the same stuff in the filler neck ,its just condnsation . the oil psi should be alright ,what kind of guage are you using ?(auto meter,etc )and is it mechanical or electronic .i started with cheap mechanical auto guage at first and they were not the most accurate now i use autometer z series electronic and they are pretty accurate and i dont have an oil line in the cab that could burst and squirt 180 degree oil all over at 100 psi.

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dman1049


Newbie
Posts: 9
posted March 15, 2011 10:53 PM

i dont know the brand but they are mechanical.

       
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mattraver


Revvin Up
Posts: 95
posted March 15, 2011 10:59 PM

get a set of electronic, they are safer and accurate auto meter or vdo are alright for the $.are you using a 3 pod cluster (oil psi,water temp and volts)?

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