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Post by ramonthebiker on Aug 5, 2023 15:34:11 GMT
A couple of years ago I went up a jet size on my Moto Guzzi Le Mans III delOrto carbs because of ethanol fuel and it runs much better. I have a CB400N and am refurbishing the carbs on it and wonder if I should increase from the 78 and 108 jets it has for Main and Secondary. Has any one done this with good results? What sizes would anyone recommend? Thnx, Ray
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Post by BritPete on Aug 5, 2023 18:20:34 GMT
That’s an interesting question and I look forward to the views from members
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Post by marktrower on Aug 5, 2023 18:48:19 GMT
hello it all depends on how you ride the bikes ,i found out a long time ago manufacturers set there bikes up on the lean side from new as the last new bike i had was in 1979 most did not have the exhaust it was born with so it was the first mod i did was up the jets i found the main was the jet to change unless i was having problems adjusting the pilot side.i went one size up on my 400 about 10 years ago now but after a run out this year when we had are summer the superdream got very hot after trying to keep up going to a bike night .the bike as run on e10 fine plodding about but that night i was wanting full power so it was between 6 to 9000 for about 9 miles .the next day i checked the plugs and they were on the lean side so what you are saying e10 makes the bike run leaner and the answer is yes
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willy3pigs
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Posts: 326
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Post by willy3pigs on Aug 5, 2023 19:38:31 GMT
I run a non standard intake and exhaust set up on my 250 and anticipated much experimentation with the jetting, and hence I fitted allen bolts to the float bowls to facilitate changing the jets in situ, as removing the carbs to do so soon gets tiresome. As I found it a worthwhile mod I did the same when I got my 400. I fitted longer bolts with spacers on the two innermost positions as it can be a right cow locating them with the allen key when they are on the bike otherwise. I also had to make a new adjuster knob to clear the extended bolts on my 250, on my 400 this wasn't an issue. I run an 80 and 110 set up on my 400 and it runs just fine with the plugs showing a good colour. Pic of my 250 carbs showing modified fixings below..  |
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Post by buster on Aug 6, 2023 10:28:37 GMT
my personal opinion on this is make sure the standard jets are well sorted and working. Mr Honda and Mr Keihin most likely spent an inordinate amount of time (probably at a race track) tuning those carbs to suit the bike. when they did make minor tweaks over the years they NEVER changed just the jets, the needles changed too. I love the idea that joe spod in his shed knows better than honda and keihin combined. worth remembering the basic principle of a carburettor, IF YOU DRAW MORE AIR THROUGH IT, IT WILL SUPPLY MORE FUEL.
sorry for shouting but this subject is a real pet peeve for me
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Post by ramonthebiker on Aug 6, 2023 10:36:29 GMT
for sure the carbs should work well and the jets not need alterations unless substantial changes to the rest of the system - eg taking off the air filter or exhaust. But did those respected designers foresee ethanol being added to petrol and the removal of lead? I certainly don’t know if it will make a difference on a Honda hence my question but I know my Guzzi runs better. Currently on my Honda the pipes are tinted blue and it does not run well. So refurbishing and tuning the carbs optimally is of course the first step… but I will try a size up on the jets out of interest and report back 👍
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Post by marktrower on Aug 6, 2023 11:45:20 GMT
It is a fact e10 is not as efficient as e5 and none e fuel but you will not see these drawbacks nipping around on a sonny day.the bike was designed 40 years ago and the 3 value head was honda trying to make the engine more efficient not to get more mpg but to make it pass the emissions especially the USA and Europe. Things have changed over my superdreams lifetime it still has a two into two exhaust but not a honda one the airfilter is not honda and the biggest change is the fuel so most of are bikes are not what they were 40 years ago so suttle changes may be made and jets are not expensive. The superdream is no faster with bigger jets it just feels better at higher rpm and runs cooler
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Post by BritPete on Aug 8, 2023 7:19:23 GMT
I run a non standard intake and exhaust set up on my 250 and anticipated much experimentation with the jetting, and hence I fitted allen bolts to the float bowls to facilitate changing the jets in situ, as removing the carbs to do so soon gets tiresome. As I found it a worthwhile mod I did the same when I got my 400. I fitted longer bolts with spacers on the two innermost positions as it can be a right cow locating them with the allen key when they are on the bike otherwise. I also had to make a new adjuster knob to clear the extended bolts on my 250, on my 400 this wasn't an issue. I run an 80 and 110 set up on my 400 and it runs just fine with the plugs showing a good colour. Pic of my 250 carbs showing modified fixings below.. Like the inner screw mod - wish I had thought of it  |
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Post by marktrower on Aug 8, 2023 10:12:28 GMT
Hello buster except for moto gp and F1 the majority of motorsport is done by jo spud in his shed and some get unbelievable results. Why have forums well I go on them well most of the bikes I get are around 20 year old and all have issues so I read and ask questions example a vtr1000 I am on with was told to go up a jet size and lift the needle 2 change the cam chain tensioners for manual ones change the ignition coils for stick coils take the restrictors out of the inlet manifolds and this information is from jo spuds that have put put more track time and development hours in than honda have.just my rant
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Post by buster on Aug 9, 2023 12:09:01 GMT
I'm not saying that bikes cant be improved Mark.
the original question at the start of the thread was about jet sizes and I expressed my opinion (something we are all entitled to do?) on that subject specifically and I stand by what I said. in my opinion you will gain nothing from increasing jet sizes, has your regular riding route started taking you over the top of Mont Blanc? have you significantly increased the capacity of your engine? if the answers no to those questions then the carburettors are pretty much self adjusting, again I'll make the point, if you pull more air through them they will supply more fuel.
a separate issue that crops up occasionally on the forum is how to get the CV's to work with pod filters, I only mention it because I dont believe that anyones ever solved that issue with bigger jets.
although the bike I took on the derbyshire run may look fairly standard on the face of it, it is actually quite heavily modified in a few carefully chosen areas and yes it has taken a lot of development (by this joe spod, in the garage at home) I'v still got a slightly irritating flat spot around 3500rpm (and no upping the jets wont cure it) but its possibly worth repeating what a couple of the 400n riders said to me on the run
'kinell that thing pulls well dunnit?
bloody hell that thing goes well
isnt there a saying in racing that lean is mean?
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Post by marktrower on Aug 9, 2023 19:46:07 GMT
i have no problem with opinions,if a bike is as was from the factory i would say check other things burt they are not most have aftermarket parts fitted fuel injection is able to adjust the fueling but a carb is preset it cannot adjust its mixture.e10 is not as efficient but you will not notice the difference until you make the engine work hard.a main jet is supplys a pre set measure through the size of the jet and the taper of the needle if this setup is not supplying enough fuel and the carb is clean and 100% working order you have got to ask yourself what as changed we know the fuel has and we would be very lucky if we are still running a honda exhaust system and a change of system can alter things considerably all this nocks things out of sink as i said modern fuel systems self learn and can adjust to an extent but a carb will only give what it is set up to give.i went one size up on the main jet about 12 years ago now the bike is no faster but is smoother on the top end. but a hot day when are summer was here on a fast run to a bike night the bike was very hot that hot the oil light was flashing on tickover checket the plugs pics were put on this site i have a box full of jets when i have time i will swap them it may improve the running it may not as i have worked on competition engines for over 40 years now i do not think i will be wasting my time.and your are right buster cv carbs do not work without a airbox
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Post by marktrower on Aug 11, 2023 18:53:10 GMT
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Post by marktrower on Aug 11, 2023 18:58:59 GMT
i forgot the small washer is another way of adjusting the main jet needle they lift the needle up get them of ebay the ones that hold computer circuit boards down are ideal
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Post by marktrower on Aug 12, 2023 19:20:59 GMT
gave the bike a run out it pulls better in the higher gears and is stronger up to 9000rpm and is stronger in top gear.i have no interest in going faster but if i can make it get there two seconds quicker i would be over the moon took the plug out on the rich side but a lot better than before   |
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Post by marktrower on Aug 14, 2023 12:53:39 GMT
gave the bike another run out yesterday pulls better at between 5 to 9000 adjusted the pilot side but the factory settings are fine .i have ordered two 112 from jet plus i believe the 115 are a tad to big over fueling is not good for a race bike the 115 will be fine but to much for the road.the pilot side is ok with standard setup if you want to go up with the main jet 112 is as big as you want to go if you do not go over 6k in the higher gears you will not feel a difference.at £8 for a set of jets to the door and 1/2 hour of your time its worth doing
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